The retiring president of the Roman Catholic hierarchy in this country yesterday urges his church to concentrate on evangelizing the substantial number of lukewarm Catholic in its fold.

Pointing out that there are "many" in thee Catholic Church "who have never experienced true conversation," Archbishop Joseph L. Bernardin of Cincinnati told fellow bishops that their missionary work begin at home.

"Realistically, we cannot envisage a successful effort ot evangelize others on a large scale - for example, the 80 million unchurched in the United States - when so many Catholics themselves have set to experience conversation," the archbishop said in his valedictory as president of the National Conference of Catholic Bishops.

Bernardin concentrated on the fundamental question of the faith-life of the nation's 49 million Catholics to the virtual exclusion of the many social, political and economic questions that have occupied the church in three years he has been president of the U.S. hierarchy.

He noted only in passing that "we should not hesitate to apply Christ's teaching" to such secular issues. He warned, however, that "as bishops we cannot claim to have any special expertise concerning the concrete social, economic and political solutions to the problems we seek to address from a moral and spiritual . . . perpective."

In a press conference, Bishop Raymond A.Lucker of New Ulm, Minn., one of thee American delegates of last month's worldwide Synod of Bishops in Rome, speculated that "perhaps 75 per cent" of American Catholics may not be "converted, faith-filled followers of Jesus Christ" and thus prime candidates for evangelization.

Such Catholics, he said, "have been baptized" into the church and may even attend Mass "but they have never turned their lives over to the lord.

The use of such language and talk of "conversation", terms long familiar to evangelical Protestants, is relatively new in the Catholic Church, which he protrayed as a lifelong prochurch through the sacraments of baptism - usually in infancy - and confirmation.

Bernardin's call for evangelization of the church's lukewarm members, which he potrayed as a process of spiritual growth, was linked to the major project before the bishops as they began their annual four-day meeting here. They are slated to complete a national catechetical directory - a 254-page summary of the essentials of Catholic belief today, coupled with guidelines on communicating the faith to peopl of all ages.

Such a directory was mandated by the Vatican Council in 1965 to reflect-the new understandings of the Christian faith reached at that historic session.

The final draft before the bishops here represents a four-year effort and the broadest consultative attempt ever undetaken by the church in this country. More than 90,000 suggestions from lay experts - have been sifted through to develop the draft.

The bishops have submitted 304 amendments to the directory to debate this week, with 114 coming from Bishop Thomas J.Welsh of Arlington who is fighting to make the document more conservative.

In this address, Bernardin called "close relationships" between the bishops, who constitute the "teaching authority" of the church, and "theologians and social scientists.

There have been numerous clashes in the church in recent years between the bishops and scholars whose studies have led them to advocate positions, particularly on moral issues, beyond the traditional stance of the church.