Thousands of animal rights activists and their allies marched to the U.S. Capitol yesterday in a show of strength intended to persuade the federal government to regulate the use of animals more strictly for research and food production.

The turnout for the march -- 24,000, according to U.S. Park Police -- was large enough to erase the image of animal rights activists as "cranks, extremists . . . a part of the lunatic fringe," said Peter Linck, one of the rally's organizers. "The animal rights movement has arrived, and we're not going away."

The marchers carried placards and chanted slogans expressing their opposition to what they contend is the needless suffering of animals for the benefit of humans in medical research, meat processing and the testing of cosmetics.

The crowd made it clear that they want rapid change, and that there is little room for compromise. They even booed Superman, actor Christopher Reeve, when he encouraged moderation.

Reeve, one of several celebrities from the movie and music industries who addressed the rally, said the use of some animals in research, such as in AIDS research, is not bad as long as it is properly regulated.

Nor, Reeve said, is everyone who breeds animals and uses them in research a villain.

"If you want to get things done, the worst thing that can happen to you is to be identified as the fringe," Reeve said.

A chorus of boos rose again, and Reeve left the podium.

Several people in the crowd said moderation is ill-advised, especially because Louis Sullivan, secretary of the U.S. Department of Health and Human Services, called animal rights activists "terrorists" at a news conference last week.

"Reeve has a right to his opinion, but this was the wrong place for him to speak about it," said Mindy Gregg, 18, a Northern Virginia resident who also has worked with the homeless and has attended anti-apartheid demonstrations.

More than three dozen animal rights groups from at least 25 states, Israel, Canada and Australia participated in a rally on the Ellipse and a march down Pennsylvania Avenue to the west side of the Capitol. Almost every one of about four dozen demonstrators interviewed yesterday gave a similar response when asked about why they adopted animal rights instead of another cause.

"When people say 'It's only an animal,' I get really upset because animals feel the same pain we do," said Rita Eisman, of Rhode Island. "They feel hunger and thirst and they have brains. That's why we are here to speak -- because they can't speak for themselves."

Demonstrators shouted down a college student who said he represented a small group from George Washington University who support the humane use of animals in medical research.

Erik Werth, 20, a political science major, told an activist that he did not view as equal the lives of humans and animals. "I'm sorry, but if I had to choose between the life of a human and a rat, I am going to take the human," Werth said.

One demonstrator shouted back: "That's your choice. I think they are both equal."

Canvas and plastic shoes, cotton T-shirts and shorts were the attire of choice of the marchers. And almost no one carried a leather bag or wore anything made from an animal's skin.

One woman, Kathy Brady, of New York City, said she was sorry the crowd was almost exclusively white.

Many, such as Sukey Leeds of New York City, have long been active in the animal rights movement.

Leeds, an animal rights activist for 20 years, said she was saddened because little progress has occurred. And she criticized organizers for allowing only three women to speak.

"Women have done all the work in the animal rights movement -- the spirit of animal rights is a female perspective, but men really run it and they have for years," said Leeds, who is also active in women's and gay rights.

One woman went to the rally because she thought it would be a good place to find a home for a cat she had found. She was wrong.

The woman, who asked not to be identified, was carrying the gray cat in a box with a sign that said "I need a home." But before the marchers strode off toward the Capitol, about 20 people surrounded the woman. One of them played tug of war with the woman -- with the cat as the rope.

"Gimme that cat!" the demonstrator said, apparently believing that the cat was dehydrated and needed to be taken for medical attention.

A police officer intervened.

"I don't understand it," the woman with the cat said. "These people are crazy. I just want to find a home for the cat. I don't want him to go to a shelter."

When the officer let the woman leave with the cat, some in the group insulted him and said he didn't care about animals.

"You're wrong," the officer said. "I've got two cats, two rabbits, a bird and a wife that wanted to be here today but couldn't because she had to be with her mother."

Casting director Rosemary Welden, 42, and housepainter Jim Gilbert, 47, of Venice, Calif., came to the rally with a 200-member contingent from that state.

They said while they have been active in other causes, they have concentrated the majority of their efforts on animal rights in the past several years.

"People used to think of animal rights supporters as a bunch of crazy old ladies in tennis shoes," Welden said. "But these are professionals -- doctors, lawyers, teachers. I think this will make history because it is the first time people from all walks of life have come together for animals and to speak out."