Thousands of antiabortion demonstrators braved freezing temperatures on the Mall and rising concerns about wartime security yesterday to hold their annual rally against the 1973 Supreme Court decision that legalized abortion.

Police estimated that about 25,000 people participated in the March for Life, down from last year's crowd of 75,000. Nellie Gray, president of March for Life, said that "well over 50,000" people took part in activities yesterday, compared with about 200,000 last year. Police and protest organizers use different methods of counting and their totals often diverge.

Many people stayed away because of concerns about the threat of terrorist activity in Washington, demonstrators said. Patricia Eklund, 44, a nurse who came with a group of about 90 demonstrators from Holy Redeemer Church in Freeport, N.Y., said that 10 to 15 people from her area canceled because of concern about terrorism.

"They thought Washington wasn't the smartest place to be right now," Eklund said.

Another demonstrator, Peggy Homberger of Pomona, N.Y., said the importance of the rally's message outweighed the threat of a terrorist attack. "We are more concerned about terrorism of the womb," she said.

Waving bright yellow placards that declared "The Natural Choice Is Life," demonstrators rallied at noon around a speaker's platform erected on the Mall near Seventh Street and tried to keep warm in temperatures that were in the 20s.

They rubbed their hands. They shifted their weight from one leg to another. One woman guided her baby's stroller in a circle, apparently hoping that the movement would keep her child quiet and warm.

This year's demonstration, the 18th since the Supreme Court ruling, came amid new struggles over the abortion issue at the federal and state level.

In Congress, the antiabortion groups are pressing for legislation that would overturn the Roe v. Wade abortion-rights decision handed down Jan. 22, 1973. They also are supporting bills in several states, including Utah and Maryland, that would impose restrictions on abortions.

And, at a news conference yesterday, John C. Willke, president of another antiabortion group, the National Right to Life Committee, told of the effort he and other activists are making to keep RU 486, the French abortion pill, out of the United States.

The stated theme of yesterday's March for Life was "no more waffling on the life principles." Gray said that politicians no longer will be allowed to get away with waffling on the abortion issue by trying to agree with both sides. Those who do will be defeated at the polls, she said.

Clad in a red coat and headgear, Gray presided over the rally. Among the first speakers she introduced was President Bush, talking by a telephone hookup from the White House.

The president, who traditionally has addressed this demonstration, said the antiabortion cause is making progress but has much work to do.

"Abortion on demand continues unabated in this country," Bush said. "And as I have said in the past, this prevalence calls into question our respect for the fundamental right to life."

Bush made no reference to the gulf war, but several other speakers drew comparisons between their personal war against abortion and this country's war against Iraq. Rep. Chris Smith (R-N.J.) said he found in the gulf war two valuable lessons.

"The first lesson is the lesson of cost," he said. "Are we willing to pay whatever it takes to achieve protection for the unborn? I believe we are . . . . The second lesson we ought to glean from Operation Desert Storm involves the crafting of a prudent strategy coupled with total commitment.

"No more Vietnams, the president said last week. No more limited engagements. I say, 'Amen to that.' With {abortion} casualties exceeding 25 million children dead . . . let us pray, let us fast, let us work as never before, to fight in a way so as to win."

Daniel Nichols, 37, a letter carrier from Warrington, Va., who was among the demonstrators, also made a point of linking abortion with the gulf war.

"If you accept the principle that it's all right to kill an innocent baby, which is what's happening in America with abortion every day, then there's nothing to stop you from bombing an Iraqi baby," Nichols said in an interview.

The rally also heard from former president Reagan, whose letter was read aloud by former Reagan intern John Taylor.

"There is no need for reasoning or rationalizing the life principles; our goal is that of saving the unborn," the letter said.

After the rally, antiabortion marchers began their trek up Constitution Avenue to Capitol Hill. Waiting for them at Constitution and Fourth Street was a group of about 50 people from the National Organization for Women, holding up posters that said "Keep Abortion Alive" and large panels that displayed the signatures of more than 25,000 Americans who support abortion rights.

As the antiabortion marchers passed the NOW group, police moved their squad cars between the groups. The march continued without incident.

At the Cannon House Office Building, Marcia Palmer of Toms River, N.J., arrived with several other demonstrators to see their representative, Frank Pallone (D-N.J.).

Palmer said Pallone was a "turncoat in the truest sense of the word," because he ran as an antiabortion candidate in 1988 but later switched to an abortion-rights position.

"We gave him our votes and then he changed his mind," Palmer said.

Pallone was not in his office to meet with Palmer or the other demonstrators. An aide spoke to the group and answered questions for about 30 minutes.

The aide said Pallone was at his district office in New Jersey.

Staff writers Paul Duggan, Eric Charles May, Avis Thomas-Lester and Maralee Schwartz contributed to this report.