Theology, says the Rev. Charles E. Curran, "should always be in dialogue with the world . . . should always be in tension with the church."

In the last few years, there has been a little more tension than he bargained for, because the Vatican, after a six-year investigation, told him to retract his views on birth control and certain other questions of sexual ethics if he wants to continue teaching theology at Catholic University.

Curran, 51, went public last week with details of his long-running battle with the Vatican's Congregation for the Doctrine of the Faith, once known as the Inquisition, and its president, Cardinal Joseph Ratzinger.

Curran, who has been at CU since 1965, is no stranger to controversy. In 1967, when CU trustees tried to fire him because of his liberal views, a five-day strike by students forced the school to renew his contract.

The next year, he was in trouble again as the chief spokesman for about 600 Catholic theologians around the country who argued that, contrary to papal encyclicals, couples could in some circumstances use artificial birth control and remain good Catholics.

A CU faculty board of inquiry exonerated Curran.

"But this is much more serious than 1968," he said of his current difficulties. "This is intervention by the Holy See."

For Catholics, this is not just some arcane scholarly dispute in ivied university walls.

In the conservative-liberal polarization among Catholics since the Second Vatican Council, Curran has increasingly emerged as the lightning rod for right-wing Catholics' ire at the modernization in their church.

Right-wing publications of the church have inveighed against him for years, urging readers to write the Vatican demanding his removal. Some bishops have banned him from speaking in their dioceses.

He even appears as one of the villains in a contemporary novel that attacks post-Vatican II reforms in the church.

He has learned to live with it. "Just by temperament I'm not a brooder. Some people get a bad review and they anguish over it. With me, three days later I've forgotten about it," he said in an interview last week.

He added, "I try to be respectful of other people's positions."

He even defends Cardinal Ratzinger, his current antagonist. "The role of Cardinal Ratzinger, by definition, is to hold onto tradition, maybe a little more than I would like . . . . Mine as a theologian is constantly to probe and to push."

But while he is respectful of other people's opinions, his years of attacks from the right have made him quick to respond.

His public lectures at Catholic University and elsewhere often attract off-campus visitors who wait to catch him in a damaging doctrinal position that can be added to his dossier in Rome.

After a campus lecture by Curran on the public policy aspects of abortion during the 1984 presidential campaign, a questioner, with an air that suggested he had cornered his quarry, asked if Curran's position did not disagree with St. Thomas Aquinas.

Curran paused -- just long enough to suggest he had indeed been caught out -- then cited a passage from Aquinas justifying his position, summarized it, and quoted the pertinent phrases -- in Latin.

His students, most of whom call him Charlie, consider him to be not only a stimulating, witty teacher but also a friend and, especially for the seminarians he teaches, a role model who participates in campus liturgies.

Curran takes pains to point out that he respects "the need for a hierarchical teaching office of the church," but he emphasizes that his differences with Rome involve his dissent from noninfallible church teaching.

"Infalliblility is like pregnancy; either you are or you aren't," and if the teachings are not infallible, theologians, in his view, have the right to "respectful, responsible dissent," he said.

Curran's carefully nuanced departures from church teachings are characterized by fellow theologians as "really very conservative."

He holds, for example, that contraception and sterilization "are not intrinsically evil but can be good or evil insofar as they are governed by the principles of responsible parenthood and stewardship."

On abortion he believes that "truly individual human life" begins not at conception but with the process of individuation, which occurs two to three weeks later. But he warns, "One can be justified in taking truly individual life only for the sake of the life of the mother or for a value commensurate with life itself."

Sexuality, he believes, "should be seen in terms of the female-male relationship," but adds that "for an irreversible, constitutional, or genuine homosexual, homosexual acts in the context of a loving relationship striving for permanence can in a certain sense be objectively morally acceptable."

Like most priest faculty members at CU, Curran lives on campus, in a two-room suite in Caldwell Hall, above the theology offices and classrooms. "It's the only coed dorm on campus," he quipped, pointing out that nuns are housed in one wing of the building.

He spends a good bit of his nonteaching time on the road, lecturing and leading seminars and retreats all over the country. For recreation, he said, "I read; I see a play about once a month." In the summer, he permits himself a couple of weeks of golfing vacation.

If the Vatican process plays itself out against Curran, he will be removed from the CU theological faculty. The opprobrium of a formal Vatican censure would also mean the end of invitations to lead workshops and retreats. Coming back from one such session recently, he recalled, "I said to myself, 'It might be the last time I'll ever do that.' "

But he spends little time on self-pity. If the "worst-case scenario" should come to pass, he wonders what would happen to the scholarly discipline he loves and to which he has devoted his life.

"There's no doubt we've put together the best Catholic faculty in the United States" at CU, he said. If he is forced out by the Vatican, "It certainly would cause some people to rethink" whether they will continue at the school.

"It's a shame," he mused. "You just wish it just didn't have to be."

Curran, recognized as one of the foremost theologians of the day, says he would not have trouble finding another job. "I've had many offers to leave this place," which he turned down "because of my commitment to what could be done here . . . . "

"I have enough trust in God and in God's way . . . and in my own ability. I think I can land on my feet."

Still, he added softly, "It sort of hurts at times."