A CBS NewsNew York Times poll, meanwhile, finds the vast majority of Americans continues to believe that abortion should remain available in at least some cases.
Seventy-seven percent of respondents said abortion should either be generally available, or available but with stricter limits than now. Just 22 percent said abortion should not be permitted.
In Washington, anti-abortion activists by the thousands marched with banners and placards in sub-freezing weather Wednesday, buoyed by hopes that the new Republican-run Congress will curb the procedure.
But only a small number of demonstrators marked the aniversary in front of Dr. Barnett Slepian's old office near Buffalo, reports CBS News Correspondent Jim Axelrod.
Slepian was an abortion provider shot to death in 1998 -- an example of how abortion is redder than any other red-meat social issue in America.
But for all the shooting, bombings and rallies in the last 30 years the abortion rate now, two percent for women of reproductive age - is about the same as the mid-70's.
President Bush was marking the anniversary by long distance, reports CBS News Correspondent Mark Knoller.
The president, who already has promised to sign any bill that restricts late-term abortions, chose the 30th anniversary to declare the United States "must protect the lives of innocent children waiting to be born."
Mr. Bush, who was in St. Louis to give a speech on his tax-cut plan, noted in a broadcast hookup that the gathering on the National Mall was near the memorial to Thomas Jefferson, author of the Declaration of Independence.
"The March for Life upholds the self-evident truth of that declaration - that all are created equal, and given the unalienable rights of life, liberty and the pursuit of happiness," he said.
Though Mr. Bush is clearly opposed to abortion, he doesn't discuss it frequently. During his first two years in office, he's only mentioned abortion in four speeches. He appears to recognize that it is a divisive issue: Last year, he urged that those who support abortion rights should be treated with respect and civility.
This year's anniversary is the first since Republicans regained control of the Senate in the November elections. The GOP also holds the House and the White House.
A host of pro-choice organizations had people on the streets in counter-protest. But several anti-abortion rights protesters said they saw new energy in their own ranks, bolstered by the changing political climate and youthful exhuberance.
"It just seems like it's more optimistic this year after the November elections," said Dennis Voglesong, 50, of Hagerstown, Md., who was attending his fifth March for Life. "I see a lot more kids here this year. Every year it seems the youth gets to be a larger part of the movement."
Wednesday's events attracted tens of thousands of participants. They included priests, nuns, political leaders. Men, women and children of all ages came as well, and both the anti-abortion and pro-choice movements were well represented.
"Most anniversaries are causes for celebration," said Philadelphia Roman Catholic Archbishop Anthony Bevilacqua. "This one is not. It is a day of mourning. Mourning for this immoral, unjust, illogical decision."
Bevilacqua, who chairs an anti-abortion committee of the U.S. Conference of Catholic Bishops, led an all-night vigil Tuesday night at the Basilica of the National Shrine of the Immaculate Conception. About 7,000 people, including five cardinals, 36 bishops and 250 priests, attended the annual "Mass for Life" and prayer service.
Across town, meanwhile, NARAL Pro-Choice America hosted a dinner attended by 1,300 people, featuring Democratic presidential candidates, including former Vermont Gov. Howard Dean, Rep. Dick Gephardt of Missouri and Sens. John Edwards of North Carolina, John Kerry of Massachusetts and Joseph Lieberman of Connecticut.
In their first joint appearance, the presidential hopefuls pledged to protect abortion rights.
"There is nothing moral in strong-arming a personal belief, and there is nothing moral to a presidency that imposes personal morality through acts of government power," Gephardt said.
Gephardt and Edwards discussed the importance of passing a federal law to guarantee abortion rights even if the Supreme Court should overturn the 1972 Roe decision.
"The right to choose is an essential ingredient to realize the full equality of America," Edwards said.
Abortion-rights supporters are concerned that the Republican control — coupled with the possibility of a retirement from the Supreme Court this year — increases the chances that Roe v. Wade could be eroded or overturned. The high court now is split 5-4 in favor of abortion rights.
Kim Gandy, president of the National Organization for Women, said her group's focus will be on maintaining the current Supreme Court balance and ensuring that "we will not be the generation that both won and lost reproductive rights in our lifetime."
Whether in favor of abortion or against it, the issue drew thousands to various events throughout the week.
Also Wednesday, the Feminist Majority Foundation began a two-day conference with more than 400 college students who will discuss ways to maintain abortion rights.
Weary after a 15-hour drive from Evansville, Ind., Carolyn Pfender, 59, said she came to Washington to be heard by politicians and justices.
"It's like murder when they abort a child. Who are we to put an end to it?" she said.
It's not that nothing's changed in the last 30 years - plenty has, says Axelrod. The number of U.S. counties with no abortion providers is up. The number of extreme harassment cases for providers and patients is down.
Contraception is more readily available, and apparently more effectively used: abortions are down 11 percent for all women, and down more than double that for teenaged girls. It's just that the battle lines seem so fixed.
"The reasons abortions are done," said Wanda Franz of the National Right To Life Committee, "are for reasons of social.. and emotional.. and lifestyle
"I think no matter how many stories you hear about women using knitting needles and hangers... you just... when you grow up in a generation that has access to abortion... you cannot conceptualize it," said student Allison Attenello.
It's somewhat ironic considering how tenuous the situation is, says Axelrod. After 30 years of back and forth, the culture hasn't moved decisively in one direction or another. Roe V. Wade is still a Supreme Court justice's heart away from being overturned.