Marking the fifth anniversary of the assassination of Archbishop Oscar Romero of El Salvador, 30 American and Canadian religious leaders have called on President Reagan to give a lift to the stalled Contadora peace negotiations in Central America.

The appeal by the religious leaders -- including heads or officials of 13 major Protestant denominations, seven Catholic bishops, and the ecumenical councils of the United States and Canada -- launched a week of religious activities commemorating the March 24, 1980, death-squad slaying of Romero. The prelate has become a symbol of resistance against oppression in Central America. During the week, churches in several cities declared themselves as "sanctuaries" for illegal refugees.

Hundreds of people signed "pledges of resistance" to engage in civil disobedience if the United States significantly escalates its military role in the region.

"We ask that you stop encouraging the process of militarization. We invite you to move immediately to cooperate with and strengthen regional Latin American efforts for peace through the Contadora process," the religious leaders wrote in a letter to Reagan.

"Contadora" refers to the four Latin American nations -- Colombia, Panama, Venezuela, and Mexico -- that have been drafting a treaty to reach a political resolution to conflicts in Central America.

As a result of Contadora efforts in the past year, the letter said, "new possibilities for peace have emerged. The Contadora countries have made great diplomatic efforts to prevent 'accidental wars,' to remove the Central American conflicts from an East-West [U.S.-Soviet] context, and to provide a basis whereby the different countries may live in security side-by-side despite economic and political diversity."

The letter cited a draft treaty worked out last September between the Contadora and Central American nations and "aimed at eliminating or reducing foreign military bases, exercises, advisers, and arms transfers and establishing measures to bar the undermining of one government by the other."

The religious leaders also pointed to recent negotiations between the Salvadoran government and leftist rebels, and statements by political and religious leaders, in support of political, rather than military, solutions to Central American strife.

However, they continued, "In spite of all these voices, numerous blocks have thwarted both the Contadora process . . . . What sounds abstract on paper -- AC47 gunships and howitzers -- translates into more defenseless peasants being killed and more villages destroyed. The suffering intensifies hourly."

Among U.S. leaders signing the letter were the Most Rev. John M. Allin, presiding bishop, Episcopal Church; Dr. Arie Brouwer, general secretary, National Council of Churches; Dr. Avery Post, president, United Church of Christ; the Rev. Kenneth L. Teegarden, general minister and president, Christian Church (Disciples of Christ) and Bishop James M. Ault, president, Board of Global Ministries, United Methodist Church.

Other U.S. signers included the Rev. Robert C. Campbell, general secretary, American Baptist Churches, and Catholic Bishops Walter Sullivan of Richmond, Thomas Gumbleton of Detroit, Maurice Dingman of Des Moines, and Frank Murphy of Baltimore.