Leaders of mainline Protestant denominations mapped a unified strategy here yesterday against South African apartheid, listing tactics that include increased pressure for additional U.S. economic sanctions and further efforts to force U.S. businesses and banks out of that nation.

Branding the system of racial segregation "an unmitigated evil . . . and the work of the devil," more than 125 church leaders meeting at the National City Christian Church proclaimed this "the year of action by U.S. churches against apartheid."

They established plans to turn longtime anti-apartheid sentiment expressed by individual churches into mass marches, lobbying efforts and selective buying campaigns "against those corporations which refuse to disassociate themselves from apartheid," according to a statement.

The group said it hopes to use moral suasion in U.S. corporate board rooms to try to force U.S. businesses out of South Africa.

It also said it will try to persuade U.S. banks not to roll over $14 billion in short-term loans to South Africa, which froze payments on foreign debts in August and is seeking to negotiate repayment.

The meeting was intended to follow up one last month in Harare, Zimbabwe, where the World Council of Churches gathered about 50 top church leaders from North and South America, Europe, Asia and Africa. They met with 45 South African Christians to explore problems stemming from apartheid.

"We were asked [by South Africans at Harare] to put the brakes on more resolutions and rather to strategize" on ways American churches could pressure the U.S. government to act effectively against apartheid, said the Rev. Avery Post, president of the United Church of Christ and cochairman of yesterday's conference.

"South Africans have completely lost confidence in the United States as a responsible government in relation to their cause," he said.

The Rev. Mance Jackson, secretary of the Board of Social Concerns of the Christian Methodist Episcopal Church, added that South Africans maintained in Harare that "it is the U.S. government and the governments of France and Britain that keeps apartheid alive . . . .

"They said to us, 'Our people are dying because of your government. We are dying because [U.S.] church people are not putting pressure on your government,' " he said.

Participants yesterday came largely from U.S. member churches of the WCC, and the group established a Churches' Emergency Committee on Southern Africa. Post expressed hope that non-WCC churches, including Roman Catholics and evangelical Protestants, would participate.