DISRUPTIVE DEMONSTRATIONS against abortion clinics here and elsewhere are compelling the courts to define, once more, what the limits of lawful protest are. In a constructive decision in Alexandria last week, Federal Judge J. Clavitt Clarke Jr. permanently enjoined 11 right-to-life demonstrators from invading a clinic in Fairfax County or harassing or intimidating people entering or leaving the clinic. The judge will specify soon where picketing may occur. In a separate Montgomery County case, five persons were convicted of trepassing for staying in a Rockville clinic after employees and police had asked them to leave.

At issue in these cases is more than the ability of any particular abortion clinic to operate in peace. Like some civil-rights and anti-war demonstrations before them, these protests raise the perennial question of how far citizen may freely go in opposing a law or policy that they believe is immoral or unjust.

The position of many anti-abortion or pro-life groups is summed up by the Rev. Robert J. Henle of St. Louis University in a letter on this page today. "If one is convinced that abortion is a violation of the primary and most sacred civil and human right," he declares, "then one tries to reduce the number of abortions and thereby save as many human lives as possible."

Rev. Henle's letter was prompted by our recent editorial opposing curbs on federal funding of abortions. But some who share his belief have not confined themselved to undeniably proper means of expression such as petitioning Congress and demonstrating peacefully on public property. In Fairfax County, Rockville and elsewhere, pro-life groups have repeatedly invaded or obstructed abortion clinics and harassed their patients and staff. Such activities may indeed prevent some abortions. But they also interfere with other citizens' exercise of a right - the right to choose to have an abortion - which has been affirmed by the Supreme Court.

On may or may not agree with the Rev. Henle that, in time, the court's decision "will be classed with the Dred Scott decision" as a denial decision is now law. Those who choose to act in accord with it should be protected against harassment or physical attack. And those who oppose it have the option always available to moral dissenters in this society: to keep their protests within legal bounds, or choose the course of civil disobedience and accept the penalties.

A crucial question, of course, is just where the boundaries of lawful protest are. In Northern Virginia and elsewhere, that has not been clear. In recent months two Fairfax County judges have acquitted anti-abortion demonstrators of trespassing charges, causing Commonwealth's Attorney Robert Horan to stop bringing such charges. That had been seen by pro-life groups as a green light for their disruptive activities. And that is why Judge Clarke's decision is significant. He is trying to establish firm, reasonable ground rules, and tell all those involved in this dispute what protection - or prosecution - they may expect.