Guatemala has broken ranks with U.S. allies in Central America to adopt a neutral position in regional peace talks just as the United States moves to take over the process.

The shift by the conservative Guatemalan government in effect bolsters Nicaragua's leftist Sandinista government, and their combined resistance to U.S. blandishments again has put the so-called Contadora treaty process on hold.

The State Department yesterday endorsed a new Contadora treaty draft composed by Honduras, El Salvador and Costa Rica with U.S. advice, calling it "a positive and constructive step" toward settling regional disputes. Nicaragua, however, has accepted an earlier draft and refused to agree to any changes.

Guatemala was represented at the Oct. 19-20 meeting in Honduras that produced the most recent draft but did not propose amendments and did not endorse the product, Federico Fahsen, Guatemala's ambassador to the United States, said yesterday.

He said that was partly because Nicaragua was not represented at the meeting. "We did not sign any document, and in fact our attitude prevented the other countries from signing communiques," he said. "Anything acceptable to all four other Central American nations would then be acceptable to us."

The new draft and the overall Contadora peace process -- named for the Panamanian island where Mexico, Venezuela, Panama and Colombia first met to launch the talks -- is expected to be among chief topics of discussion when Latin American foreign ministers assemble Monday in Brasilia, Brazil, for a meeting of the Organization of American States.

Secretary of State George P. Shultz leaves here today for that gathering and is scheduled to speak at Monday's plenary session. He plans to have breakfast Monday morning with the foreign ministers of the "Core Four," the nations of Central America other than Nicaragua.

Shultz is expected again to urge Guatemalan Foreign Minister Fernando Andrade to back the U.S. position that the treaty must have very strong verification mechanisms to be worthwhile.

The new draft, composed to address U.S. concerns, would set up independent teams of roving inspectors to check each country's compliance with treaty terms requiring disarmament, closure of foreign bases and departure of all foreign troops and advisers.

Such a system would be unprecedented in Central America, but State Department officials are known to feel that any treaty without such a system, in effect, would license Cuba and Nicaragua to aid leftist guerrillas throughout the hemisphere.

The officials say Nicaragua's desire to rid itself of U.S.-backed rebels who raid from Honduras would allow Nicaragua to agree to inspectors.

In fact, however, the new proposal almost certainly will require "several months of study" by all parties, as one Central American diplomat put it, effectively stalling the Contadora process indefinitely.

Guatemala's position arises in part from its annoyance at continued U.S. criticism of its human-rights record and U.S. hesitation in supplying arms to its rightist government.

A secret briefing paper prepared for a National Security Council meeting Oct. 30 noted that the "uncertain support" of Guatemala "is a continuing problem."

It listed efforts by Shultz, other U.S. officials and Salvadoran President Jose Napoleon Duarte to persuade Andrade and Guatemalan President Oscar Mejia Victores to back the U.S. position.

"Serious personality problems between Honduran Foreign Minister Edgardo Paz Barnica and Andrade continue to hamper efforts to keep the Core Four together," the memo said. "We will continue to exert strong pressure on Guatemala to support the basic Core Four position."

Fahsen discounted the notion of any personality clashes, noting that the five heads of state had chosen Andrade to speak for them before the European Economic Community earlier this year. "The problem is that Guatemala does not dutifully follow anybody but follows its own interests," he said.

He denied receiving any U.S. pressure. "They are trying to strengthen certain parts of the treaty according to their views," Fahsen said.

"We won't take an active role in trying to change the treaty one way or the other. We will accept the verdict of the other four countries. If we're going to sign something, it is all five of us," he added.