Braving stiff winds and an icy drizzle, thousands of people led by Mayor Adrian M. Fenty marched to the U.S. Capitol yesterday in the biggest demonstration in decades for full representation for the District in Congress.

"Free D.C.! Free D.C.!" chanted the activists, who thronged several blocks of Pennsylvania Avenue, marching past fluttering red-and-white District flags and U.S. flags. They waved signs reading "I Demand the Vote," "Democracy Starts at Home" and -- in a nod to the foul weather -- "Getting Wet to Get a Vote."

Organizers estimated the turnout at up to 5,000 people. Terrance W. Gainer, the Senate sergeant-at-arms, said the crowd numbered roughly 3,500. That would make the demonstration the biggest voting-rights rally in decades, and possibly the largest ever, organizers said.

The march occurred at the start of a week in which House Democrats expect to approve a bill giving the District its first full seat in that chamber. The measure then would go to the Senate, where it probably will face a tougher fight.

It was not clear whether the march would temper strong opposition to the bill by some leading Republicans and the White House, which has threatened a veto. But the demonstration could help keep the issue on Congress's front burner at a time when politicians are consumed by the Iraq war and other issues, analysts said.

"The more you can keep a public focus on an issue, the better it is in terms of raising the sensitivity of members of Congress to push it a little higher in the queue," said Norman J. Ornstein, a political scientist at the American Enterprise Institute.

Marchers made it clear they would keep up the pressure.

"We're gonna go to the White House next!" yelled Fenty (D), addressing the marchers after they reached the Reflecting Pool in front of the Capitol.

"White House next! White House next!" chanted the crowd.

The voting-rights bill, sponsored by Del. Eleanor Holmes Norton (D-D.C.) and Rep. Thomas M. Davis III (R-Va.), adds two seats to the House of Representatives. One would go to the overwhelmingly Democratic District, and the other to the next state in line to get an additional representative: Utah, a Republican stronghold.

Many activists said they will continue pushing until the District gets two senators as well as the House representative.

The event began with a rally at city hall, featuring Fenty, former mayor Anthony A. Williams (D), members of the D.C. Council and Norton, who can vote in House committees but not on final legislation. It was held on Emancipation Day, which marks the freeing of slaves in the District.

A variety of participants arrived in vans, school buses and cars: senior citizens, civil rights activists, union workers, college students and church members. Many were involved either with city-funded groups or with DC Vote, an advocacy group that played a key role in planning the event. Some said the city had provided transportation.

"This was an important day in the history of D.C.," said D.C. Council member Harry Thomas Jr. (D-Ward 5). "The citizens came out despite the weather to show that this is an important day for us."

Marchers said they hoped the event would further mobilize residents.

"The sad fact is, we've been too passive," said the Rev. Clark Lobenstine, executive director of the Interfaith Conference of Metropolitan Washington, as he approached the Capitol and a light rain began to fall.

The march did encounter some problems. With wind gusts of up to 60 mph downing power lines and closing some schools in the area, the rally at the Capitol was cut short. A number of prominent speakers, including several congressmen, did not make it. Organizers said the weather undoubtedly dampened turnout.

And, as Fenty, Norton and Council Chairman Vincent C. Gray (D) led marchers down Pennsylvania Avenue, holding a banner that read: "First Freed. Then Taxed. Still No Vote," another group of demonstrators repeatedly jumped in front of the procession with their own banner: "Fenty -- Let us vote on the school takeover."

Fenty's security detail and march organizers formed a protective semicircle around the dignitaries and pushed away the demonstrators, who oppose the mayor's plan to assume control of the city school system.

But overall, the mood was upbeat. Demonstrators rang cowbells and cheered speeches by Fenty, Norton and Gray. Even though she is 83 and nursing a cold, the D.C. statehood activist known as Faith rode on top of a car and blew her bugle during the procession.

Stacie Goffin, an education consultant in her 50s, said she became interested in the issue after moving to the District seven years ago from Kansas. "I want the vote. I get what it feels like" to have it, said the Dupont Circle resident.

Helen Rehwaldt, 32, a chef who lives near American University, said news of the march was "all over the city" in recent days. "It was a great turnout, given how horrible it was outside," she said.

Fenty seized on the symbolism of the city's Emancipation Day, a District holiday, to rally city residents around the voting issue. He threw himself into getting a big turnout, sending recorded telephone messages to D.C. residents, distributing thousands of fliers through the city's political networks and even printing news of the march on city employees' pay stubs. Since taking office in January, Fenty has made voting rights a top priority.

A spokesman for the Republican leader in the House, John A. Boehner (Ohio), said his objections to the bill remain unchanged.

"House Republicans are not opposed to giving D.C. residents representation in Congress. But they are opposed to running roughshod over the Constitution," said the spokesman, Brian Kennedy.

Critics, including some prominent legal experts, say the bill violates the constitutional requirement that House representatives come from states. Supporters of the legislation, including other legal scholars, rest their arguments on another constitutional provision giving Congress sweeping powers over the District.