Mary Pat Miller of State College, Pa., has been to Washington before. Along with an estimated 50,000 to 60,000 people from across the country, she marched again yesterday from the Elipse to the Capitol in the eighth annual March for Life to protest the landmark 1973 Supreme Court decision permitting women to have abortions in some cases.

Like so many others marching with her, she comes to the nation's capitol each year to take part in this enduring rite of winter in a town where the only permanent thing seems to be change.

"I have five children, and I happen to feel that a child is the most precious thing there is," Miller said. "So every year I get my Penn State blanket and a thermos of hot chocolate, and I come down here, and I plan to keep coming."

Presidents come and go, the Congress shifts from liberal to conservative, and still the issue of abortion tugs at the national conscience.

This year could have been different. They had a chance to meet with the man they consider their champion -- Ronald Reagan -- in his White House office, but they turned him down because he had refused to come out and address their rally.

Bearing antiabortion banners, red roses, rosaries and cardboard babies tacked to plywood crosses, the protesters stood in ankle-deep mud on the Ellipse and listened to an array of speakers espousing antiabortion themes.

On stage, Jeff Steinberg of Memphis, Tenn., entertained the crowd by singing Christian music and patriotic songs. Steinberg, who was born with no left arm and missing knee joints received cheers from the crowd when he told them, "I'm glad God loved me enough to let me come into His World."

He also told the assembly that those who really liked his songs could purchase copies of his record album from his van -- parked just a few feet from the stage.

Following Steinberg, March for Life president Nellie Gray told the group to remain diligent in their efforts to add a Human Life Amendment to the Constitution and to continue lobbying members of Congress to that end. The amendment would call for protection of human life from the moment of fertilization and forbid any practice that would terminate that life.

Gray then introduced several anti-abortion legislators including Sen. Jesse Helms (R-NC.) and Rep. Robert K. Dornan, (R-Calif.), cosponsors of the so-called Paramount Human Life Amendment.

Opponents of the amendment say it would not only make abortion illegal but ban some popular forms of birth control such as the low-estrogen birth control pill and the inter-uterine device (IUD), which are often though to work after fertilization has taken place.

But many who took part in yesterday's march said banning abortion -- not contraception -- is their goal.

Charles Williams of the Long Island, N.Y., chapter of Right to Life, said, "We have never taken a position on any form of contraception. We are interested in preserving a life after it begins, but I think the choice to start that life is a personal matter between a husband and wife." t

After an hour of song and speeches, the crowd recited an antiabortion version of the Pledge of Allegiance, which promises liberty and justice for all, "born and preborn," and headed down Pennsylvania Avenue.

Their first stop was the White House, where many expressed their displeasure that President Reagan, who has spoken in favor of an antiabortion amendment to the Constitution, did not come out to join the march or at least to address it's participants.

"We sent him an invitation right after the [Republican National] Convention," Gray said, "and we renewed it on Nov. 20. Tonight, you may hear that some leaders of the right to life movement met with President Reagan today, but I decided to turn down the invitation, because I feel my place is out here on the front line."

Later, a March for Life spokesman said no member of the organization has ever met with a president, and added, "We're glad she [Gray] did not go to the White House. If Reagan wants to meet some prolife people, he should have come across the street."