Tens of thousands of abortion protesters, some carrying signs that said "American Holocaust" and "I regret my abortion," marched from the White House to the Supreme Court on Thursday to mark the 31st anniversary of the decision that established a woman's right to the procedure.

"Abortion kills more people than war," said 14-year-old Andrew Marshall, who traveled with his family and a Catholic youth group from McMurrey, Pa. "We're trying to win a war in America, it's a war to stop abortion."

The day of activism — including events both for and against the court's 1973 ruling in Roe v. Wade (search) — began with a mass and anti-abortion rally attended by nearly two-dozen Catholic bishops and a crowd of about 15,000, most of them teenagers.

"The theme of this day is human life and human dignity," Cardinal Justin F. Rigali, archbishop of Philadelphia, said before the rally.

A smaller group of abortion rights activists said they largely focused on lobbying on Capitol Hill for legislation to reverse limits on reproductive freedom imposed since 1973.

They planned their own march for reproductive rights (search) on April 25.

President Bush called in a brief statement, telling the anti-abortion marchers they were gathered for "a noble cause."

"The right to life does not come from government, it comes from the creator of life," the president said by telephone from Roswell, N.M., where he was wrapping up a two-day trip.

Terry McAuliffe, chairman of the Democratic National Committee, said abortion rights were at risk because of Bush's decisions, "from stacking the federal judiciary with anti-choice proponents, to executive orders, to regulations, to restrictive legislation and key political appointments."

"Anti-choice zealots want to impose their views and theology on the rest of us, and that's just not right," said Gloria Feldt, president of the Planned Parenthood Federation of America (search).

Outside the Supreme Court, Luana Stoltemberg, 43, of Davenport, Iowa, held the "regret" sign. She said abortions had contributed to her inability to have children when she wanted them. She later adopted.

"I've had three abortions, and that hurts women like me," she said. "It devastates us physically, mentally, spiritually and emotionally."