The Rev. Thomas D. Campbell, a strong backer of reunification of the white and black denominations of the Cumberland Presbyterian Church, was elected moderator of the white church group Monday.

Campbell, a Knoxville, Tenn., pastor, is author of "One Family Under God," a book dealing with reunification of the two branches of the Cumberland Presbyterians, which held their general assembly here.

The predominantly white Cumberland Presbyterian Church and the mostly black Second Cumberland Presbyterian Church, founded by former slaves in 1874, tried to move closer to unification during their meetings. Joint worship services were held and committees tried to determine how blacks and whites will be represented on church agencies of the proposed unified church.

The Cumberland Presbyterians, with 90,000 members, dwarf the 8,000-member black denomination. Named for the mountain area of Tennessee and Kentucky where it was born, the church grew out of a split with the larger Presbyterian group, now called the Presbyterian Church (U.S.A.) in 1810.

Campbell, the new moderator, was the founding pastor of St. Luke Cumberland Presbyterian Church in Fort Worth and St. Matthew Cumberland Presbyterian Church in Burleson, Tex. He also holds a master's degree and doctorate from Brite Divinity School in Fort Worth.

Campbell's election was a case of history repeating itself. His father, the Rev. Thomas H. Campbell, was elected moderator in 1973, the only other time the national meeting of the denomination was held in Fort Worth.

"I have a feeling my father is enjoying this somewhere," said the new moderator, who won by a vote of 60 to 25 over the Rev. Edward B. Hollenbeck of Benton, Ark.