For prosecuting attorneys everywhere there is, as they say, good news and bad news. The good news: Dan Sheehan is beginning a one-year monastic period to prepare to become a Jesuit priest. The bad news: Dan Sheehan will be back.

Sheehan is the 32-year-old attorney who scored a crucial victory this summer for the Church of Scientology, currently involved in a bitter legal wrestling match with the government. Federal prosecutors alleged that church members conspired to burglarize government offices, steal government property and obstruct criminal investigations. Sheehan borrowed space in a friend's law office, labeled the prosecutorial efforts as "political," and won a front page decision tow months ago; a federal judge ruled materials seized by the FBI in a raid of the church's Washington office be returned because the search warrant was unconstitutionally broad. The case is likely to drag on for years, but round one went to Sheehan, who charged no fee for his work.

Neither controversy nor victory is new to Sheehan, a Massachusetts native who looks like a young Michael Landon and talks like a cocky street-fighter about his cases. While still a law student at Harvard in the late Sixties, Sheehan helped prepare the case that set an important precedent for draft age men: a person didn't have to prove he believed in a Supreme Being in order to be classified a conscientious objector. In the summer of '68 Sheehan organized a Biafran relief effort by cajoling free airplanes and food from corporations and convincing wary diplomats the planes should be allowed to make their mercy flights.

Then he convinced the Massachusetts Supreme Court that the state's anti-birth control law was unconstitutional. ("What's a good Irish boy like you doing arguing a case like this?" one judge asked the devoutly Catholic Sheehan.)

In '70 Sheehan went to work for a pricey New York law firm and promptly got involved in the Earl Caldwell case, the Attica prison mess and the Pentagon Papers case. But he thinks his outside work on behalf of prisoners at the Tombs irritated his bosses, and he was fired.

Sheehan realized he was a lawyer for causes, not corporations, and he next represented a California missionary group arrested in Montana on charges of traveling to Wounded Knee to aid radical Indians. Actually, says Sheehan, the group was carrying medicine. His victory there led him to other cases involving Indian causes. Then to ACLU, civil rights and more religious legal battles.

Sheehan is now a candidate for the priesthood. He lives outside Washington on a $145 monthly stipend from the Jesuits (they provide his housing and meals) and is winding down his role in the Scientology case. Next stop: a monastary in Oregon where Sheehan will put aside his lawbooks for the Bible. He found that his concept of law as a tool for promoting social justice coincided with the Jesuit outlook on the world, and he intends to combine the two in a couple of years as Father Sheehan, for the defense.