The event drew demonstrators from across the country, and many said that in addition to taking their discontent to the streets they planned to press members of Congress to oppose the war.

“When we voted it was a directive to bring our troops home now,” said the Rev. Graylan S. Hagler of Plymouth Congregational United Church of Christ in Washington, referring to the November elections when Democrats won control of Congress.

Demonstrators listened to speeches from a roster of politicians and entertainment figures including the Rev.Jesse Jackson; Representative Dennis J. Kucinich, Democrat of Ohio and a candidate for the presidency in 2008; and Representative Maxine Waters, Democrat of California. The actors Jane Fonda, Susan Sarandon and Tim Robbins also addressed the crowd.

“We need to be talking not just about defunding the war but also about funding the vets,” Ms. Sarandon said, adding that more than 50,000 had sought treatment through the Department of Veterans Affairs while benefits for them continue to be cut.

With Mr. Bush facing low approval ratings and Congress continuing to debate the terms of a nonbinding resolution opposing the troop increase, elderly people in wheelchairs, housewives pushing strollers, seasoned dissenters in tie-dye and veterans in uniform turned out to protest.

“I grew up during the Vietnam War, but I never protested it and never had my lottery number called to go fight,” said David Quinly, a 54-year-old carpenter from Prairie Village, Kan., who arrived here Friday night with about 50 others after a 23-hour bus ride.

“In my view, this one is a war of choice and a war for profit against a culture and people we don’t understand,” Mr. Quinly said. “I knew I had to speak up this time.”

Along the north side of the Mall, teenagers in T-shirts featuring sinister depictions of Mr. Bush chanted, “End the lunacy; end it now.” A man wearing prison stripes carried a sign with the likeness of Vice President Dick Cheney. A man on 30-inch stilts, dressed asAbraham Lincoln, carried a sign quoting him: “But you can’t fool all of the people all of the time.” A tall, clear plastic column stood overflowing with thousands of shoes symbolizing the civilians killed in the war.

“I’ve got a son who just got out of the military and another still in,” said Jackie Smith, 65, from Sunapee, N.H., whose sign read “Bush Bin Lyin.” “And I’m here because this is all I can do to try to help them.”

Tassi McKee, from Bastrop, La., who said she was a staff sergeant in the Air Force, was among a small contingent of about 20 active-duty service members who turned out. “I believe this has become a civil war, and we are being hurt and making matters worse by staying in the middle of it,” Sergeant McKee said.

She said that it was not illegal for active-duty members to attend protests but that it was strongly discouraged.

Veterans were more numerous among the crowd.

Dressed in the olive green, military-issued flight jacket that he said he wore during the invasion of Iraq while serving as a Marine sergeant, Jack Teller, 26, said he joined a caravan from Greenville, N.C., because he felt that it was his duty.

“I don’t like wearing the jacket because it reminds me that I participated in an immoral and illegal war,” said Mr. Teller, who had “Iraq Veterans Against the War” stenciled on the back of his jacket. “But it’s important to make a political statement.”

Fernando Braga, a 24-year-old Bronx native who is a member of the Army National Guard, said that he was skeptical of the war before it started. Mr. Braga said his views hardened into opposition while he served in Iraq from March 2004 through January 2005.

“My own commander told us when we arrived that if we thought we were there for any reason other than oil then we had another think coming,” he said. “I realized even commanding officers were against it but following orders.”

Michael McPhearson, executive director of Veterans for Peace, said more than 100 veterans from the Iraq war participated in the march, and several hundred veterans from previous wars attended as well.

Robert Watada, 67, of Honolulu, a retired executive with the State of Hawaii who said his son, First Lt. Ehren K. Watada, was to be court-martialed next month for refusing to deploy to Iraq, said: “So many thousands of our own have died and hundreds of thousands of Iraqis and for what? And still we are having to push Congress to block the president.”

At least 3,065 American military personnel have been killed and at least 22,834 have been wounded since the start of the war in March 2003, according to Iraq Coalition Casualty Count, a Web site that tracks Department of Defense numbers. The United Nations has estimated that at least 35,000 Iraqis have been killed each year since the war started.

President Bush, who often spends weekends at Camp David, was in Washington on Saturday but had no public events scheduled. He spent part of the morning on his weekly bicycle ride at a Secret Service training facility in Beltsville, Md.

The White House issued a statement in response to the demonstration. “The president believes that the right to free speech is one of the greatest freedoms in our country,” said Gordon D. Johndroe, a White House spokesman. “He understands that Americans want to see a conclusion to the war in Iraq, and the new strategy is designed to do just that,” referring to Mr. Bush’s plan to increase troop levels in Iraq.

The protest was largely organized by the group United for Peace and Justice, a coalition of 1,400 local and national organizations.

“This war has been going on longer than she has been alive, and Cheney says it will be a 50-year war,” said Annie Yanowitz, a housewife from Amherst, Mass., pointing to her 2-year-old daughter, Amira.

“I find that totally inappropriate that our children may grow up with this war continuing,” Ms. Yanowitz said.

Police officials declined to provide crowd estimates, but Hany Khalil, a spokesman for United for Peace and Justice, said the protesters numbered about 400,000. Smaller antiwar protests took place on Saturday in other cities, including San Francisco, Los Angeles and Sacramento.

In Washington, counterprotesters also converged on the mall in smaller numbers, but the antiwar demonstration was largely peaceful.

There were a few tense moments, however, including an encounter involving Joshua Sparling, 25, who was on crutches and who said he was a corporal with the 82nd Airborne Division and lost his right leg below the knee in Ramadi, Iraq. Mr. Sparling spoke at a smaller rally held earlier in the day at the United States Navy Memorial, and voiced his support for the administration’s policies in Iraq.

Later, as antiwar protesters passed where he and his group were standing, words were exchanged and one of the antiwar protestors spit at the ground near Mr. Sparling; he spit back.

Capitol police made the antiwar protestors walk farther away from the counterprotesters.

“These are not Americans as far as I’m concerned,” Mr. Sparling said.

Another counterprotester, Larry Stark, 71, a retired Navy officer who fought in Vietnam for five years and was a prisoner of war, said, “We never lost a battle in Vietnam but we lost the war, and the same is going to be true in Iraq if these protesters have their way.”

The protesters on Saturday were undermining troop morale, Mr. Stark said, and increasing the likelihood of a premature withdrawal.

“It’s like we never learn from the past,” he said.

The plan is the main money-saving component of Mr. Obama’s education agenda, which includes a sweeping overhaul of financial aid programs. The Congressional Budget Office says replacing subsidized loans made by private banks with direct government lending would save $94 billion over the next decade, money that Mr. Obama would use to expand Pell grants for the poorest students.

But the proposal has ignited one of the most fractious policy fights this year.

Because it would make spending on Pell grants mandatory, limiting Congressional control, powerful appropriators are balking at it. Republicans say the plan is proof that Mr. Obama is trying to vastly expand government. Democrats are divided, with lawmakers from districts where lenders are big employers already drawing battle lines.

At the same time, the private loan industry, which would have collapsed without a government rescue last year, has begun lobbying aggressively to save a program that has generated giant profits with very little risk.

“The administration has decided that it wants to capture the profits of federal student loans,” said Kevin Bruns, executive director of America’s Student Loan Providers, a trade group that is fighting Mr. Obama’s plan.

To press its case, the nation’s largest student lender, Sallie Mae, has hired two prominent lobbyists, Tony Podesta, whose brother, John, led the Obama transition, and Jamie S. Gorelick, a former deputy attorney general in the Clinton administration.

For lenders, the stakes are huge. Just last week, Sallie Mae reported that despite losing $213 million in 2008, it paid its chief executive more than $4.6 million in cash and stock and its vice chairman more than $13.2 million in cash and stock, including the use of a company plane. The company, which did not receive money under the $700 billion financial system bailout and is not subject to pay restrictions, also disbursed cash bonuses of up to $600,000 to other executives.

Sallie Mae said that executive compensation was lower in 2008 than 2007 and that the stock awards were worthless in the current market.

Critics of the subsidized loan system, called the Federal Family Education Loan Program, say private lenders have collected hefty fees for decades on loans that are risk-free because the government guarantees repayment up to 97 percent. With the government directly or indirectly financing virtually all federal student loans because of the financial crisis, the critics say there is no reason to continue a program that was intended to inject private capital into the education lending system.

Under the subsidized loan program, the government pays lenders like Citigroup, Bank of America and Sallie Mae, with both the subsidy and the maximum interest rate for borrowers set by Congress. Students are steered to the government’s direct program or to outside lenders, depending on their school’s preference.

Private lenders say they still provide valuable service, marketing, customer relations, billing, default prevention and collection of delinquent loans. The lenders say the budget savings could be achieved without ending their role and are pushing to keep the system in place, including an arrangement approved by Congress last year by which they are paid to originate loans but can resell them to the government.

Martha Holler, a spokeswoman for Sallie Mae, said the company wanted a compromise. “To be clear, there are those who are fighting to preserve the historic financing structure for federal student loans,” she wrote in an e-mail message following up on a telephone interview. “Sallie Mae is not among them. In fact, we support constructive alternatives that would generate a similar level of taxpayer savings to achieve the administration’s important goals.”

Lenders are also emphasizing the jobs they provide.

Sallie Mae’s chief executive, Albert L. Lord, held a town-hall-style meeting last week at the company’s loan center in Wilkes-Barre, Pa., with two Democrats, Senator Bob Casey and Representative Paul E. Kanjorski, to announce the return of 2,000 jobs that were sent overseas in 2007.

Mr. Lord, in his opening speech, insisted that Mr. Obama’s proposal offered new opportunities, but he said he would fight to keep the current system mostly intact.

“We can either meet or beat the budget savings that are in the president’s budget with the exact same system that we have got working now with maybe a few tweaks,” he said.

But to preserve a profitable role for private lenders and still achieve Mr. Obama’s savings seems extremely difficult if not impossible; initial projections put forward by Sallie Mae could reach only 82 percent of the president’s goal over five years.

Last year, to keep education financing from drying up, Congress expanded the government’s role, including the repurchase of loans, which Sallie Mae and some other lenders say should be mandatory going forward.

“When you add that all up, a very legitimate question to ask is why do we even need private lenders,” said Representative Timothy H. Bishop, Democrat of New York and a former provost of Southampton College.

For Mr. Bishop and many other education advocates, Mr. Obama’s plan to expand the existing direct loan program used by more than 1,500 schools is obvious and long overdue.

But the administration has a fight on its hands.