The West German cardinal who two years ago was most insistent on the Vatican's disciplining of theologian Hans Kung has replaced Cardinal Franjo Seper as head of the powerful Sacred Congregation for Faith and Morals.

Cardinal Joseph Ratsinger, 54, archbishop of Munich and Freising, was named to the post last month by Pope John Paul II. Seper, 76, who died Wednesday of a heart attack, had resigned his post of 13 years because of ill health.

The Congregation for Faith and Morals, formerly known as the Holy Office, is the ultimate arbiter of doctrine in the Catholic Church. Relatively quiescent for a decade, the congregation handled a flurry of cases in 1979, the most notable of which were those of Kung and Dutch theologian Edward Schillebeeckx, both of whom are theologians of international reknown.

Schillebeeckx was summoned before the congregation and successfully defended his views. But Kung, who had been in a long-running dispute with the Vatican over his views on papal infallibility and other issues, was told he could no longer consider himself a Catholic theologian. The decision cost him his post on the Catholic theology faculty at the University of Tuebingen and bars him from teaching at any church-controlled seminary.

It is widely believed that Ratsinger pressed the Vatican to take action on the long-simmering controversy over Kung.

The Congregation for Faith and Morals has been widely criticized for its procedures, which critics charge violate the rights of persons called before it. Persons called are not allowed counsel and frequently--as in the case of Schillebeeckx--are not informed who their accusers are or what the precise charges are against them.