SANTO DOMINGO, DOMINICAN REPUBLIC, DEC. 22 -- Efforts to restart the indirect cease-fire negotiations that began last night between the Nicaraguan government and contra rebels failed today, effectively ending the second round of talks in a month.

"We are at an impasse," said Cardinal Miguel Obando y Bravo, Nicaragua's Roman Catholic archbishop, who serves as mediator. The talks that began late yesterday broke down several hours later, at about midnight.

Both sides pledged to honor the Christmas truce planned for Thursday and Friday, which will be the first since the U.S.-supported rebels began fighting the leftist government six years ago.

Victor Hugo Tinoco, deputy foreign minister of Nicaragua, said he proposed a third round of talks for January after Obando y Bravo suggested it. Contra spokesman Bosco Matamoros said his delegation had not been notified and he would not comment.

The talks carried out through Obando collapsed in dispute over rebel insistence that Nicaragua negotiate directly with them rather than through foreign advisers, and the Sandinistas' refusal to do so. The advisers included an American lawyer and a West German legislator. "Without the presence of at least one government delegate . . . there will be no negotiation," Matamoros said.

Tinoco called the demand for direct meetings "a pretext." He said the contras agreed in advance to meet with the advisers, but changed their position when the U.S. Congress prepared to approve $8 million in new aid.