Pope John Paul II is about to appoint a new group of cardinals that is expected to include Washington Archbishop James A. Hickey, according to sources close to the Vatican.

Only once during his three-year pontificate -- in June 1979 -- has John Paul added members to the church's College of Cardinals. Since then there have been changes in the leadership of some of the church's key jurisdictions which have traditionally been presided over by a cardinal.

There was widespread speculation last spring that the appointment of new cardinals was imminent, but any action that might have been in the works at that time was cut short by the attempt on the pope's life.

Now, with the approach of the Advent, a traditional time for consistories of the College of Cardinals in which new members are inducted, and with the pope back at the Vatican full-time, reports are again circulating about new appointments.

It was learned last week that the press office of the National Conference of Catholic Bishops here is updating its biographical material on six American prelates considered possible candidates for the honor. They are, in addition to Hickey, Bishop Paul Marcinkus, longtime head of the Vatican bank who was appointed governor of Vatican City last month; the Most Rev. Edmund C. Szoka, recently named archbishop of Detroit; the Most Rev. John L. May, archbishop of St. Louis; the Most Rev. John R. Quinn, archbishop of San Francisco; and the Most Rev. Joseph L. Bernardin, archbishop of Cincinnati.

While neither Cincinnati nor San Francisco has been the seat of a cardinal in recent history, both Quinn and Bernardin have achieved worldwide notice as presidents of the bishops' conference in this country. May and Szoka both head archdioceses traditionally presided over by cardinals.

Hickey, who has had no comment on the reports, has headed the Washington archdiocese for 15 months. He succeeded Cardinal William W. Baum, who was summoned to Rome in 1980 to head the Vatican's Sacred Congregation for Catholic Education.

Currently there are six Americans serving as active cardinals; four others are retired.

Another likely candidate for the cardinal's red hat is Archbishop Jean Jadot, a Belgian, who a year ago was recalled from his post here as apostolic delegate to become pro-president of the Vatican Secretariat for Non-Christian Religions. The post is traditionally headed by a cardinal.

Two other Vatican civil servants now holding cardinal-level posts are Archbishop Giuseppe Casoria of the Sacred Congregation for Divine Worship and Archbishop Paul Poupard of the Secretariat for Non-Believers.

Other world church leaders who are virtually certain to be raised to the rank of cardinal eventually include recently named Archishops Jean-Marie Lustiger of Paris, Carlo Maria Martini of Milan, Godfried Danneels of Malines-Brussels, and Jozef Glemp, who succeeded Cardinal Stefan Wyszynski as primate of all Poland.

Both John Paul and his predecessor, Paul VI, used their office to increase representation from third world countries in the College of Cardinals. Given his widespread travels in Latin America, Africa and Asia, it is considered quite likely that John Paul's next list of appointments will include churchmen from those areas.

The Sacred College of Cardinals, which took shape in the 12th century, never exceeded more than 70 members until 1959 when Pope John XXIII set aside that limit. It reached its all-time high in 1973, when Paul VI made appointments that brought the number to 145, but also decreed that only the 120 members who were under the age of 80 could vote in the conclave to choose his successor.

Until the 1918 Code of Canon Law limited the College of Cardinals to priests, there were lay cardinals. In 1971, John XXIII decreed that cardinals must come from the ranks of the bishops.

For centuries, the sole duty of the College of Cardinals was to elect the pope. But two years ago John Paul expanded the cardinals' role, when he called an extraordinary session of the college to help him wrestle with, among other questions, the church's growing financial problems.