SANTA BARBARA, CALIF., AUG. 24 -- President Reagan is using Radio Liberacion, the clandestine station of the Nicaraguan contras, to broadcast a personal message of "peace and freedom" to the Nicaraguan people, administration officials said today.

But Reagan's message was clouded by a mixup in its announcement that gave the leftist Sandinista government of Nicaragua an opportunity to electronically "jam" the broadcast.

White House spokesman Marlin Fitzwater announced during the White House daily briefing here that the president had given the radio speech discussing the pending Central American peace proposal. After the briefing, however, Fitzwater said he was informed by officials in Washington that Reagan had not given the message yet and that now there was concern that the Sandinistas would jam the program.

"I got the day wrong and simply made a mistake in announcing it," Fitzwater said.

Several minutes later a press staff aide distributed a statement saying that the message would be released to reporters on Tuesday morning. The speech was given tonight.

A senior official who discussed what had happened on condition that he not be identified said the mixup "was not in itself any big deal but unfortunately reflects some of the problems we've been having lately in getting our message across."

Reagan is trying to walk what this official called "a tightrope" between conservatives who fear he will desert the contras and congressional Democrats who are concerned that he is simply giving lip service to proposals for a negotiated end to the Nicaraguan conflict. This balancing act has resulted in a wide variety of statements by administration officials that on some days emphasize Reagan's desire for peace and on others stress his commitment to the contras.

"They're not necessarily conflicting but they are a bit confusing," the senior official said.

Some of the confusion appears to have spilled over to this Thursday's scheduled meeting in Los Angeles between Reagan and contra leaders, including military commander Enrique Bermudez.

When the meeting was announced last week, Fitzwater said it was intended to discuss the pending Central American peace proposal but also was meant as a political signal to those concerned about the fate of the contras.

"Make no mistake about it," he said then. "We want to demonstrate to the conservative leaders and to the {contra} directorate and to the nation that the president will not desert the contras."

Today, however, some administration conservatives were grumbling that the meeting will be held too late in the day to receive much attention from the television networks. Network correspondents also complained to Fitzwater that the briefing given by the contra leaders, which is not scheduled to begin until 5:30 p.m. EDT, might conclude too late to be included on that day's evening newscasts.

Fitzwater denied that this was an attempt to play down the meeting. He said the scheduling reflected logistical problems.