U.S. Catholic bishops, signaling their intention to implement the recommendations of their pastoral letters on economic justice and nuclear arms, have appointed a layman involved in social work in the Archdiocese of Washington to become their secretary for social development and world peace.

John L. Carr, the Washington diocese's social development secretary who helped set up 13 shelters for the homeless and other programs for the poor in the District and suburban Maryland, was chosen from among 30 applicants to succeed the Rev. J. Bryan Hehir at the U.S. Catholic Conference, the bishops' public policy arm. Hehir, a principal architect of the American bishops' current policy in domestic, social and international affairs, will remain as consultant to the conference.

Hehir helped envision the moral framework for the bishops' economic and nuclear statements, and Carr's job is to "make social theory social reality," said the Rev. John Kinsella, secretary of planning for the conference and a member of the search committee.

Carr, 37, did not have the high-level federal government expertise of some applicants, nor the PhDs of others, Kinsella said. But Carr brings to the job what the bishops wanted most: practical experience at the diocesan level.

"John had the the right combination," said Kinsella, "a clear understanding of a wide range of issues . . . {and} of what the needs of the local church are."

Carr is the first layman to hold the significant secretarial post, a fact that indicates the increasingly important role Catholic laity are playing in the life of the church, Kinsella said.

Last year, in a book-length pastoral letter entitled "Economic Justice For All," U.S. bishops denounced levels of poverty and unemployment in the United States and called for the U.S. government and private industry to provide new jobs, adequate housing, food and education. Three years earlier, in another letter, the bishops called for a halt to the U.S.-Soviet arms race and a reduction in the nuclear arsenals. They also opposed virtually any use of nuclear weapons.

Their statements, which upset some conservative Catholics, were discussed in church services and at parish meetings throughout the country, and were taught in Catholic schools and colleges. "The church has done a better job at education around the pastorals than helping people take action," Carr said yesterday.

"Action" is a word Carr uses frequently, according to those who have worked with him in his six years as a key assistant to Washington Archbishop James A. Hickey. Carr helped bring to the Washington area the Gift of Peace, a home for patients with AIDS or other terminal illnesses.

"John listens. He analyzes. He builds a good plan of action and he motivates people" Hickey said. "He takes the Gospel off the shelf and puts it to work."

Carr has held more than a half-dozen jobs in the Catholic Church and in government, mostly involving domestic social programs. Prior to his arrival at the archdiocese, he was executive director of the White House Conference on Families.

Carr said working for a national organization may not provide immediate results. "But there are greater opportunities to make a difference," he said. "My mother told me if there's anyone hungry in the world {now}, it's {my} fault."