Leaders of Witness for Peace, the interfaith movement organized to oppose U.S. military intervention in Nicaragua, yesterday pledged to continue sending delegations into combat areas there despite the kidnaping last week of 29 Americans by forces identified as the CIA-aided Revolutionary Democratic Alliance.

"Our government's war in Nicaragua is a national sin and disgrace," said Jim Wallis, pastor of the Sojourners Community here and one of the founders of Witness for Peace. "It is a moral offense to our religious traditions and the best ideals of our country."

The organization, he said, will no longer "protest U.S. policy in Nicaragua from our own living rooms," referring to its strategy of sending volunteers from U.S. churches and synagogues into areas where the rebel forces known as contras are active.

In the 17 months Witness for Peace has been operating, more than 1,300 persons have made such journeys without harm. But on Aug. 6, a "Peace Flotilla" of 15 volunteers, accompanied by 14 journalists, was taken captive by rebels along the San Juan River that forms the border between Nicaragua and Costa Rica. They were released the following day.

Ed Griffin-Nolan, Nicaraguan coordinator of WFP and a member of the flotilla, said at yesterday's press conference that although there were conflicting reports as to the identity of their captors, he was convinced that they were members of ARDE, the Spanish acronym for the Revolutionary Democratic Alliance, headed by the former Sandinista commander Eden Pastora.

Three Roman Catholic bishops, a Benedictine prioress, a rabbi and the head of the United Church of Christ, all of whom serve on the WFP advisory board, took turns at castigating the Reagan administration policy of military aid to the contra groups seeking to overthrow the government of Nicaragua.

"Our government supports terrorism of the worst form" in supporting the rebels, said Bishop Walter Sullivan of Richmond. "On the one hand we condemn terrorism" in many parts of the world "and yet we support terrorism" in Nicaragua, he said.

The Rev. Avery Post, president of the United Church of Christ, said the opposition of churches in this country to intervention in Nicaragua "is seriously underestimated by the U.S. government."

The religious leaders conceded that not all churches in this country agree with their position. But Auxiliary Bishop Thomas Gumbleton of Detroit noted, "You could have said that there was a split in the church in Germany" over Nazi treatment of the Jews.

The strategy of Witness for Peace is to send U.S. volunteers "at the invitation of Nicaraguan Christians" to live and work and "share the lives of ordinary Nicaraguan people" for two-week periods, explained Dick Taylor, a member of the WFP steering committee.

Despite the hazards, he said, "we believe that those who work for peace must be willing to take the same risks as those who fight in war . . . . And we cannot sit by and watch as our Nicaraguan neighbors and our Christian brothers and sisters are maimed and killed because of our government's policy."

Asked if the kidnaping last week had "frightened off" the WFP, Taylor said, "We have people signed up the rest of this year and all the way through 1986."