Watching the rare and impressive diversity of the more than 70,000 people who came to this city for last month's anti-abortion March for Life, I was reminded of the canny assessment made in 1979 by Michael Harrington, the socialist writer and organizer: "anti-abortion gatherings like this represent "one of the few genuine social movements of the 1970s."

The coalition now includes the radical right with the radical left and the extreme moderates in the middle, old- timer anti-war protesters with first- time pro-life activists, religious fundamentalists with the unchurched, people who have adopted unwanted children with those who believe that, with 1.5 million abortions a year, the womb is a dangerous place to be.

Halfway through the 1980s and 12 years after the Supreme Court ruling on fetal life, the coalition is stronger. Ronald Reagan, for once, had his facts right when he told the marchers that "momentum is with us. . . . There are already signs that we've changed the public attitude on abortion."

The most obvious change is that labels are disappearing. A decade ago, the pro-life movement was dismissed as only Roman Catholic. The church, with its set-in-stone dogmas, was out to impose its beliefs on secular society. That was a misperception then, and it is less credible today.

The energies of conservative Southern Baptists and northern liberal evangelicals such as Jim Wallis of Sojourners, as well as Jewish groups, have turned the movement into one that is truly catholic, with a small "c." A recent survey reports that 95 percent of pro-life activists are Catholic, Protestant or Jewish. More than 60 percent of pro-choice activists described themselves as having no religion.

Then it was said that the anti-abortion movement enlists only single- issue zealots. They are selectively frantic about protecting life before birth but cancel all tickets after that. It is now known -- and was on display at the Washington march -- that large numbers of those who oppose abortion also actively oppose other destruction of life: capital punishment, weapons systems, killing animals for food or fur, environmental pollution and disregard for human rights. This is the seamless-garment coalition. A commitment to end one form of violence is a commitment of consistency to oppose all forms.

Selectivity does mark the fetal politics of people such as Ronald Reagan and Sen. Jesse Helms. In their obsessions against the Soviet Union, both are ready for a nuclear abortion of the entire Earth. Judy Goldsmith of the National Organization for Women rightly knocks Reagan for his post- birth indifference to infants and mothers in the way he has cut nutritional programs for them. But that's no argument to justify abortion. It is only a so-what-else-is-new comment about presidential inconsistency.

Much harder to attack are those many members of Congress who have strong voting records on peace, labor, hunger and feminist issues but agree with Reagan about abortion. The president's selectivity is not a flaw Goldsmith should be picky about. Last year, it needs saying again, her own group passed a resolution stipulating that no one would be allowed to address future conventions unless he or she was in line with NOW's positions, including abortion. Agree with us -- or get lost.

A third argument to fall away is that abortion involves only the woman, and that her rights alone matter. In his remarks to the marchers, Reagan referred to a film, "The Silent Scream." It depicts, by means of an ultrasound camera, the violence of an actual abortion of a 12-week-old preborn child. The film, said Reagan, "provides chilling documentation of the horror of abortion during the first three months of life. It's been said that, if every member of Congress could see this film of an early abortion, Congress would move quickly to end the tragedy of abortion."

Perhaps. Congress has seen films of Hiroshima, but it votes money to build three nuclear weapons a day. The point about the abortion film is that it tells the story of another being's life under assault. The rights of the preborn are, first of all, human rights.