Groups of abortion rights activists and antiabortionists clashed in two separate confrontations yesterday in the District, outside the National Right to Life Convention where National Organization for Women members picketed and at a Northwest abortion clinic where 29 persons were arrested.

Also, on the last day of the convention, black antiabortionists called a special news conference to denounce the abortion rights movement as a form of "calculated" genocide perpetrated on blacks and other minorities and on poor people.

The day of heated protests began about 7:30 a.m. when 50 NOW members, expecting abortion protesters, lined up in front of the PreTerm Center for Reproductive Health at 1710 P St. NW.

By 8 a.m. a group of 120 antiabortionists, organized by the Pro-Life Action Network, had also arrived. They sang "We Shall Overcome" and held signs with messages such as "The unborn have no freedom of choice." By noon 29 had been arrested and charged with blocking the sidewalks.

Some of the antiabortionists wore "Choose Life" T-shirts, while NOW members wore blue sashes that said, "NOW, Witness for Women's Lives."

As the two groups pressed closer to each other, a shoving match broke out. The antiabortion protesters who blocked the entrance to the clinic were arrested. Some went limp and were carried into a police van.

Two clinic staff members met arriving patients and carefully checked their identification. Police escorted persons attempting to enter to the door of the clinic. "They're killing babies inside!" one woman yelled.

Inside the clinic everything was "very quiet," according to Terry Beresford, associate director of PreTerm. "We expected this to happen and we took steps to secure the building. We were able to provide services to everyone who came in this morning."

Nancy Cunningham, president of NOW's Bucks County, Pa., chapter, said, "We are here to assure women that they can exercise their consitutional rights."

Still, Right-to-Life organizer Monica Migliorino called the protest a success. "Women turned away . . . today; maybe they will come back," she said. "It gives the mothers a chance to rethink their decisions."

Across town, at the Hyatt Regency on Capitol Hill, 125 NOW members marched outside the hotel to protest a speech by Roman Catholic Cardinal John J. O'Connor of New York. They chanted: "Right to life remains a lie, you don't care if women die."

NOW President Judy Goldsmith said O'Connor "is joining with the antiabortionists this morning because he has utterly failed to convince even Catholic women to stop using birth control and seeking abortions." She was among marchers outside the hotel at 400 New Jersey Ave. NW.

Inside, 2,000 conventioneers crowded into a ballroom to hear O'Connor. "As much as we may fault our lawmakers . . . for the frightening state of abortion law in our land," the cardinal said, "we must, above all, ask ourselves if we really care . . . that some 4,000 babies are put to death every day in the United States."

After the speech, the National Right to Life Committee held a panel discussion and news conference on "The Issue of Abortion as It Relates to Black Americans." Erma Clardy Craven, a social worker and NRLC director of outreach to the black community, called the prochoice movement "elitist, racist and genocidal." Craven said prochoice "is a calculated move because we blacks have made too many strides in 200 years."

Panel member Carl Ellis, a member of the Chesapeake Theological Seminary faculty, said, "In the late sixties and early seventies, when family counseling programs began, it was a widespread belief among blacks that these were programs of genocide. Now, 10 years later, you don't hear that said anymore."

The black panel members said they were concerned about the prejudices of those who make any decisions on policies relating to life-and-death issues.

"We have been in the past victims of policies that devalue the value of black life," said author Samuel Yette, a Howard University professor. "A government that . . . becomes involved in the taking of life . . . may begin to define who those are who will be allowed to give life."