Leaders of Roman Catholic thought from three continents gathered here this week to explore what needs to be done to heal their ailing Church.

Officially, the theme if the four-day theological conference on the Notre Dame University campus here was: "Vatican III: The Work That Needs to be Done."

Because the participants were for the most part theologians and other scholars, rather than bishops or others in authority, the discussions will have no legislative effect on the Catholic Church or its members.

But precisely because they were not limited by official restraints, they were free to think unthinkable thoughts that sometimes flew in the face of Church doctrine and tradition.

The problems facing the Church have been so often hashed over that little time was spent discussing them: the decline in attendance at mass, the diminishing number of priests and nuns and even more serious, the critical lack of religious vocations among the young: the general exodus of young people from the Church, and, overall, the disillusionment of so many of the faithful with the institutional Church.

Theologian Hans Kueng summed it up: "Many Christians are saying; 'Jesus, yes; the Church, no;'"

The crisis of the Church, he explained, is "like the energy crisis; people are not aware of its seriousness, of what's coming out of it. In five years they will know," he predicted, asserting: "In 10 years, it will be a catastrophe."

Deploring the "exodus" of young people from the churches, Anton van den Boogaard of Holland observed that "the young will not be willing to participate until a structural change has taken place, until the present closed structure (of the Church) has been transformed into a open structure."

On the crisis of the clergy, the Rev. Dr. Eugene Kennedy of Loyola University in Chicago, pointed out: "We're staffing our parishes now with middle-aged clergy . . . In 10 years, two-thirds of our priests will be over 45."

Some of the scholars concentrated on analyzing the ills of the Church today while others proposed remedies. A sprinkling of social scientists presented the fruits of their research on the kind of world in which the Church exists today - in many respects, radically different from a thousand or two thousand years ago when doctrine first was enunciated:

"When my grandmother was born," reported demographer Teresa Sullivan, "she faced the probability of living one or two years alone with her husband" - before the children were born and after they were grown - "and six years of widowhood."

With smaller families and extended life expectancy today. "I can expect to live 21.5 years alone with my husband and face 8 years of widowhood," said Sullivan.

What are the implications of such changes for the Church's sexual ethics, several persons asked. None had an answer.

The worldwide nature of the Catholic Church was seen as raising its own set of problems. The Rev. Dr. Jacques Pohier, a Dominican moral theologian and a specialist in pyschoanalysis, posed the question of whether the moal rule in a given area can and should be the same at the same time for all the individuals and all the cultural and ethnic groups" throughout the worldwide Church.

For example, he pointed out, "sexual activity does not have the same meaning for a 15-year-old, a 30-year-old, or a 60-year-old. But neither does it have the same meaning for people living in Chicago in 1977, for peasants in India in 1977, for the Christians of Corinth of the first century, and for the seminomadic tribes of the time of Abraham."

(There were discussion, incidentally, on why the Catholic Church spends so much of its time on sexual morality.)

Proposals for Church change were legion. The Rev. Dr. Peter Huizing, a professor of canon law in The Netherlands, called for widespread change in Church law.

"Vatican II neglected to translate its teachings into the Church institutions," he pointed out. "Doctrinal statements on collegiality of bishops, responsibility of laymen, nature of Christian marriage, do not work if they are not translated into the Church institutions."

The Dutch Jesuit called for a number of changes in canon law:

The removal of questions of personal faith from the jurisdiction of canon law: "Nobody has the right to impose faith or articles of faith or the profession of faith on anybody else," he said.

Canons must recognize "the possibility of contravention of the law for the food of men," in accordance with Jesus' attitude toward law.

The removal of Church annulment procedures, dispensation of celibacy or solemn religious vows from canon law. "These matters should be left to the local churches," he suggested.

Abolition of such titles as "Holy See," "Holy Father," "Vicar of Christ," "No normal pope or cardinal or other official of the Roman curia lives under the impression that he personally or they all together are holier than any other Christian may be; nevertheless they continue making the whole church community ashamed and ridiculous by claiming such titles . . ."

Others, including the controversial Swiss theologian, kueng, proposed other reforms, a mandatory retirement age for popes as well as bishops; election - and periodic re-election - of top Church officials, including bishops and members of the Curia; abolition of mandatory celibacy for priests, lifting of the Catholic Church's ban against intercommunication, and a constant re-examination of Church practice and doctrine to be sure they are rooted in Christian principles.

The group of nearly 70 scholars had no illusions about their dreams coming true at any time in the foreseeable future. "It was not our purpose to prepare for Vatican III as of any given date," explained the priest-sociologist, Andrew Greeley, one of the organizers of the conference. "It was our purpose to point out the work that has to be done within the Church - if there is a Council and if there isn't a Council."