For the 12th year in a row, thousands of antiabortion protesters gathered in Washington to protest the Supreme Court's decision in Roe v. Wade, which legalized abortion. This year, the peaceful demonstration took place against a backdrop of growing terrorism against clinics, and to their credit, numerous speakers, including President Reagan, used the occasion to deplore the violence and the tactics of terrorists, some of whom believe they are communing directly with God.

The same day the marchers assembled in Washington, two of three suspects arrested over the weekend in connection with eight clinic bombings in Washington, Maryland and Virginia, were ordered held without bail pending further hearings and one of them has subsequently had bond set. A third suspect has been released on $250,000 bond, with strict limitations on his movements and activities.

The Bureau of Alcohol, Tobacco and Firearms has solved 20 of the 31 bombings that have taken place since May 1982, a remarkably high percentage compared to the arrest and conviction rates in other crimes. Judges have meted out stiff jail terms, running as long as 20 years. From the president on down, the forces that maintain the social order established in this country are taking the terrorism very, very seriously and moving swifly to apprehend the bombers and put them away.

Which is the way it should be: this kind of activity threatens the very core of the social order. The principal difference between fundamentalist Christians bombing abortion clinics in the United States and fundamentalist Moslems bombing buildings in Lebanon is a matter of degree of destruction. What they have in common is religious fanaticism, arguably the most destructive force in the history of civilization.

In modern times, at least, Americans have never had much truck with religious fanaticism or terrorism, whether perpetrated by the Ku Klux Klan or the Weather Underground. However critical we are of the way government and the courts move, most of us generally prefer the way we conduct our nation's business to any other system that's come along, and we take a dim view of those who are bent on securing their particular ends through intimidation and destruction.

No one from the mainstream antiabortion movement has been linked to the clinic bombings, and leaders of the movement have condemned them. They have been far more tolerant, however, toward the picketers who have been harassing patients at women's clinics. At a recent press conference sponsored by the National Organization for Women, several clinic counselors described the fear in which they now live and work.

Last May, said Kathryn Wood, the Women's Community Health Center in Huntsville, Ala., received its first bomb threat, and pickets showed up a week later. "In mid-June, an intruder entered the clinic during regular office hours," said Wood. "He was yelling, 'Let me at the machines,' and calling us murderers. He threw paint on the walls, and tried to enter the room in which abortions were being performed. I was afraid for our patients' lives, and tried to block his way. He threw me against a wall, and I blacked out. Injuries to my neck have already required surgery."

Wood filed a warrant for the man's arrest, which meant antiabortionists were able to get her name. In July, she said, several of her neighbors received letters linking her to "a vicious baby-killing ring." In August, neighbors received a letter containing a threat to bomb Wood's home. She says her teen-age children have been insulted in school.

Jeanne Clark, executive director of the Allegheny Women's Center in Pittsburgh, described picketing at the clinic during the past year as "terribly abusive," with pickets trying to prevent patients from getting out of their cars, handing out frightening literature, and targeting teen-age patients, "the ones least able to deal with stress and carry pregnancies to term."

No one argues with the right of the antiabortionists to assemble and protest peacefully, and any law that curbed their activities at clinics would meet tough constitutional challenges. But there is undeniable evidence that at least in some areas pickets are more interested in intimidating patients and those providing abortions than in swaying public opinion.

Antiabortion leaders who genuinely deplore the violence at the clinics, and the tactics of some fundamentalist shock troops, would do well to distance themselves not only from the terrorism, but also to discourage climates that foster it. The step between intimidation and terrorism can be very short, indeed, and the public knows it.