Republican presidential candidate Pierre S. (Pete) du Pont IV has called for breaking diplomatic relations with Nicaragua and establishing long-term U.S. backing for the contras trying to oust the Sandinista government.

Du Pont said in a speech before the World Affairs Council in Los Angeles Monday that the Sandinistas have installed a communist government that is allowing the Soviet Union to work on "the ultimate destabilization of Mexico." The text of the speech was released by du Pont's Washington office.

Speaking before Thursday and Friday's Guatemala summit meeting among the foreign ministers of the five Central American nations, du Pont rejected the idea that the Central Americans should be left to resolve their own regional problems without the United States pressuring its allies.

"The problem of a long-term, communist presence in Central America is the United States' problem. It is ours to solve or suffer," du Pont said.

The Central American foreign ministers meet this week to discuss a plan proposed by Costa Rica President Oscar Arias, which calls in part for a cease-fire in regional conflicts, an end to foreign support for insurgents and dialogue between the governments of the region and their opposition.

The summit has been assisted by the so-called Contadora nations, whose past efforts at peace plans have failed. Du Pont said the United States cannot "affort to hide behind the fiction that the Contadora process will solve the problem."

He said the Sandinistas failed to keep commitments to install democratic systems after overthrowing Anastasio Somoza in 1979.

"As the Sandinistas persist in ignoring their commitments to their own people, and ours, the U.S. must renew its policy of freeing the Nicaraguan people from its new oppressors, and make the long-term strategic commitment needed to achieve that goal," du Pont said.

"We must make every effort to isolate the Sandinistas diplomatically, beginning by breaking diplomatic relations with their government and encouraging our allies to do the same," he said.

"If we are to bring democracy to Nicaragua, we must state openly and clearly that we are willing to talk, but are equally prepared to support those who are willing to fight," he said.