The foreign ministers of eight Latin American nations met with Secretary of State George P. Shultz yesterday to urge that the administration's push for aid to Nicaraguan rebels be replaced with a push for a regional peace treaty in Central America.

The initiative was part of what several Latin diplomats said privately was a last-ditch effort to save the stalled three-year-old peace talks and avert further militarization in Nicaragua and Honduras.

In essence, it revolves around the concept of "simultaneity," in which the United States would halt its support for the contra rebels at the same time as Nicaragua begins liberalizing its political policies. Both Nicaragua and the United States have insisted that the other act first.

The idea that both should act at the same time is central to the Contadora peace effort and to its member ministers' latest declaration, which came at the end of a Jan. 11-12 meeting in Caraballeda, Venezuela.

The ministers represented the four Contadora nations of Colombia, Mexico, Panama and Venezuela -- named for the island where they first met -- and the "Contadora support group" of Argentina, Brazil, Peru and Uruguay. The Caraballeda declaration was later endorsed by the five Central American nations, including Nicaragua, as well as Japan and the European Economic Community.

"It is a balanced proposal that takes everyone's interests into account," said Argentine Foreign Minister Dante Caputo. "We are seeking the support of the Reagan administration for it."

Latin diplomats said that the administration could best express support for the Contadora process by delaying its plan to ask Congress for at least $100 million in military and economic aid to the contras. Nicaragua would then be under additional pressure to take steps toward "national reconciliation," a U.S. code word for opening negotiations with the contras.

Thirty-one swing-vote members of Congress expressed essentially the same position in a request to President Reagan last week that he postpone asking for the aid until the Central American presidents meet in Guatemala next month.

However, administration officials have said repeatedly that they plan to introduce their aid proposal after Congress returns from its midwinter recess Feb. 18, and a senior official reaffirmed that position after yesterday's meeting.

"We don't see any incompatibility between assistance to the contras as a method of pressuring Nicaragua to live up to its commitments, and the Contadora process," the official said.

In an interview with The Washington Post yesterday, Reagan said he was going to go "all out" to try to get the rebels "the kind of aid that they must have."

However, key House Democrats have warned Reagan that the aid proposal faces tough opposition and may not pass.

In a statement, Shultz said the meeting had been "useful, positive and serious," and announced that Special Ambassador Harry Shlaudeman, who has spearheaded U.S. negotiating efforts in the region, will visit the eight nations' capitals beginning next week.

In a letter to Reagan, nine liberal Democratic senators yesterday said that the Caraballeda initiative made this "a particularly bad time" to request new aid for the contras.

"Either we will eventually have to abandon the contras and suffer a major foreign policy setback, or we will have to move to direct U.S. military involvement. Providing lethal military aid for the contras would lead us one step further toward that dead-end choice," the letter said.

It was signed by Sens. Tom Harkin of Iowa, Claiborne Pell of Rhode Island, Christopher J. Dodd of Connecticut, Gary Hart of Colorado, Paul Simon of Illinois, Alan Cranston of California, Edward M. Kennedy and John F. Kerry of Massachusetts, and Patrick J. Leahy of Vermont.