SANTA BARBARA, CALIF., AUG. 25 -- President Reagan has told the Nicaraguan contras in a radio message broadcast to Central America that he will continue supporting them until the Sandinista government lives up to its promise to restore democracy to Nicaragua.

"Your struggle has, and always will have, our support because our goal is the same -- democracy," Reagan said. "Until the people of Nicaragua are guaranteed basic liberties, I know you will keep on with the struggle. And the United States will be with you."

The three-minute message was taped in English and followed by a Spanish translation. It was broadcast twice Monday and twice today throughout Central America over Radio Liberacion, the clandestine contra station.

U.S. officials said they had been informed that the broadcast was heard in much of Nicaragua but jammed in Managua, the nation's capital, by the government.

In the message, Reagan said the pending Central America peace plan approved by five regional governments, including Nicaragua, was "an important act of faith." But he said this faith must be "tempered with realism," and he expressed skepticism that the Sandinistas would restore democracy in Nicaragua, which "they have denied you for the last eight years."

"The Sandinistas now have promised you democracy with the world as witness," Reagan said. "Like you, I hope that they keep this promise. But like you, I also know that the civil war in Nicaragua began when the Sandinistas promised you democracy but failed to meet their commitment. This struggle will end when that promise is fulfilled."

Reagan implicitly questioned the premises of the peace plan approved by the five nations in Guatemala City Aug. 7 after rejection of a peace plan offered by Reagan and House Speaker Jim Wright (D-Tex.).

The Central American proposal, referred to by Reagan as "the Guatemalan plan," calls for a simultaneous cease-fire and restoration of civil liberties.

"The Sandinistas have told us this before, and no one one believes the Sandinistas anymore," Reagan said. "Simultaneity must mean freedom up front or no deal."

The White House issued a "fact sheet" saying the contra leadership requested Reagan's radio message during a White House meeting with the president Aug. 5.

Reagan is scheduled to meet the leaders again in Los Angeles Thursday. They are to be accompanied by their military commander, Enrique Bermudez, who is to brief the president on the military situation in Nicaragua.

A $100 million U.S. appropriation providing military aid for the contras expires Sept. 30. Reagan has promised Wright that no new aid request will be made before then, and administration officials have said the determination on whether any aid request will be made will depend on progress toward democracy within Nicaragua.