More than 80,000 demonstrators, most of them women who said they had come to Washington to show their support for the Supreme Court's landmark 1973 decision to legalize abortion, filled the length of Pennsylvania Avenue between the White House and Capitol for much of yesterday afternoon.

The "March for Women's Lives," staged in reaction to the annual antiabortion march that drew 40,000 marchers to the Capitol in late January, was dominated by young women, many of them college students. Many of the marchers said they had journeyed to Washington because they feared that the antiabortion demonstrations had convinced the president, Congress and the media that a majority of Americans oppose abortions.

A festive air developed as the the march proceeded along the three-mile route under cloudless skies in unseasonable temperatures. Demonstrators, who included mothers with children and men in shirtsleeves chanted and waved large college banners and homemade signs.

"The Religious Right has the ear of the White House," said Hollis Hood, 37, a weekly newspaper editor from Houston who limped to the Capitol in her stocking feet, carrying her black cowboy boots. "They will influence the impressionable, and the tide will swing away from birth control and other important issues. I'll be paying for this trip for the next six months, but I thought it was important to come here to be counted as a defender of women's rights." It was her first demonstration.

A Washington Post-ABC poll conducted last month showed that 54 percent of Americans said they believe that women should be allowed to have an abortion on demand, an increase over the 40 percent who held that view five years ago.

District police estimated the crowd at 85,000. U.S. Park Police said 80,000. The march organizers, the National Organization for Women, announced during a rally after the march that their count was 125,000.

Yesterday's march by abortion rights supporters exceeded all previous antiabortion marches. Abortion opponents, who have marched here annually since the Supreme Court decision, attracted their largest crowd, 60,000, in 1979, according to police estimates.

Jerry Horn, a minister from Appleton, Wis., who disrupted the march outside the White House when he moved into the lines of demonstrators holding an apparent fetus over his head, was the lone person arrested yesterday, police said. He was charged with disorderly conduct, police said. Horn attended January's antiabortion march and displayed an apparent fetus that he said was 18 to 20 weeks old.

D.C. police department homicide officials said they are "looking into" how Horn obtained the apparent fetus.

When the first marchers, including NOW President Eleanor Smeal, Rep. Don Edwards (D-Calif.), actress Mary Kay Place and magazine editor Gloria Steinem, reached the west front of the Capitol about 1 p.m., demonstrators at the end of the march were still waiting to leave the Mall -- 15 blocks away.

Signs reading "Pro Choice Is Pro Life" and "May All The Men Who Vote Against Women's Right to Safe Abortion Be Pregnant" were waved by marchers who chanted, "Not the church, not the state, women must decide their fate," as they marched 15 abreast along Pennsylvania Avenue.

The march's organizers included more than 200 colleges and nearly 500 other organizations. Elizabeth Fry, 21, an art student, marched with several friends under a banner that proclaimed, "Independent Artists of the Corcoran."

"I don't condone abortions, but I feel that women should be free to choose for themselves," she said. "It is not a decision for old men with gray hair."

Becky Goldston, 23, from the University of Massachusetts, who marched with two signs taped to her jacket -- "United for Pro-Choice" and "Make Love Not War" -- said, "I felt that this was the right time in my life to come out and march. Numbers are very important today, and I wanted to be here to be counted."

Winnie Hilton, 43, an assistant to the president of a D.C. insurance company, was one of the small number of blacks who marched.

"I am aware that NOW is largely white," she said. "But this is a black women's issue, also. Abortion is a fundamental right. I am worried about the influence of the conservative right who speak for the rich and powerful."

Hilton said that for many black women the problem of survival as single parents heading households outweighed the importance of marching.

"I am here today because my four children are taking on the laundry and my husband is cooking dinner," she said.

The crowd, massed on the lawn on the west front Capitol steps for speakers, greeted former New York congresswoman Bella Abzug with chants of "Bella, Bella."

"The same people who would deny us peace and equality and the personal liberty to choose seek to impose their absolutist point of view as to what we should read, where to pray, and what kind of families we should have," Abzug said. "The protection of the right to choose whether or not to have an abortion is as precious a liberty as the right to think, to speak and to pray."

As the rally ended at about 5 p.m., Smeal called the march a success and said it drew far more participants than organizers expected.

"The glow ain't gonna wear off, don't worry about it," Smeal said in an interview. "We are already on a roll. It's empowering because women who didn't think we could do this now think they can walk on water."