A Vatican-ordered study of how priests are trained in Catholic seminaries in this country has raised fears among some Catholic academics that Rome intends to exercise tighter control over theological education.

The unprecedented study was disclosed earlier this week to U.S. bishops and heads of seminaries in a letter from Archbishop John R. Roach of St. Paul-Minneapolis, president of the American hierarchy.

Roach said the study is designed to assist seminaries "in their ongoing process of renewal" and address the Vatican's "expressed concern about the best use of personnel and resources in a situation in which higher education is becoming increasingly costly."

It is not yet clear when the study will begin or how it will be conducted, but some Catholic academics fear that it could jeopardize academic freedom at theological institutions.

The study is "dangerous and discouraging," said the Rev. Vincent Cushing, president of the Washington Theological Union in Silver Spring. "What we have seems to be a call for a study in which a number of questions are left open: What is the mandate to ensure a proper academic atmosphere" for the study. "What norms will be used? What is the accountability for the disposition of the findings? Will we be treated as American professional educators?"

The Rev. Donald Skwor, whose organization, the Conference of Major Superiors of Men, has been asked to assist with the study, which will look at about 500 seminaries with 30,000 students, said he expected the survey "will be done along the professional lines of accrediting agencies in this country."

The Vatican has long been troubled by such innovations on the American Catholic theological scene as women on seminary faculties, women students, the pooling of Catholic, Protestant and sometimes Jewish faculties and students in cooperative educational arrangements such as the local Washington Theological Consortium, several theologians pointed out.

The Rev. James Young, rector of St. Paul's College, a seminary here, said the Vatican "doesn't understand our academic system. They don't understand tenure. They don't understand why we have to advertise to fill positions . . . A lot of the things that are taken for granted in the United States academic community are foreign to the Vatican."

The study here will be directed by an American bishop who was appointed by and is directly answerable to Rome. He is Bishop John A. Marshall of Burlington, Vt., widely regarded as a theological conservative. It is part of a study of Catholic seminaries worldwide under the supervision of Cardinal William W. Baum, former Washington archbishop, who now heads the Vatican's Sacred Congregation for Education.

Several scholars have linked the worldwide study to a mood of return to orthodoxy at the Vatican in recent years. "This sort of thing has been expected by some since Christmas of '79," said one scholar who asked not to be identified. In December 1979, the Vatican, with the blessing of Pope John Paul II, disciplined theologian Hans Kung by revoking his "canonical mission," his right to teach as a Catholic theologian.

Currently, the "canonical mission"-- a sort of certification of doctrinal acceptability -- is required of faculty in a very limited number of institutions. But there is concern among Catholic academics that the Vatican plans to require all teachers of theology in Catholic institutions to hold such a certification as a qualification to teach, which many scholars view as a violation of academic freedom.

For many, the Vatican's seminary study is seen as a step in that direction.