One by one, the nine adults and two children knelt before William Cardinal Baum last Sunday and carefully inscribed their names in the book he held in his lap.

The service at the Church of SS. Paul and Augustine marked the first time in the Washington Archdiocese that the Catholic Church's new rite of Christian initiation of adults, issued in 1974, had been used here.

Joining some churches is as simple as saying "I believe." The new Catholic procedure, in contrast, involves a year-long process of study on the part or the would-be members, known as catechumens, and several rites involving both catechumens and congregations they are preparing to join.

The new rite, explained the Rev. Ray Kemp, copastor of SS. Paul and Augustine, "makes the whole community an intergral part" of initiating new members into the faith.

For the current crop of catechumens, the process began last June, when they undertook a three-month course that included an introduction to the parish and its organizations, and fundamentals of Catholic worship and practice.

In September, the catechumens were registered as members of the parish, recognized in a special Sunday eucharist, and began participating in the life of the parish. They also began an intensive 6 1/2 month study program on the Bible, church doctrine and history and the sacraments.

Last Sunday's rite at SS. Paul and Augustine climaxed this portion of the study program, when the congregation, symbolically through their priests and lay coordinator of the program, "elected" the catechumens into the church.

The ritual of membership is not completed until they are baptized during the Easter vigil service on the Saturday night before Easter.

Father Kemp praised the new rite, saying that "the 'election' highlights the call of each Christian by Christ as well as the responsibility of the Christian community to be a living sign of Christ's presence to their own members and to our un-Christian environment."