The State Department, shaken by a young guerrilla fighter's success in embarrassing the Reagan administration's efforts to prove Nicaraguan and Cuban involvement in El Salvador, hastily sent him home to Nicaragua yesterday and began studying ways to repair the damage to U.S. Central America policy.

Orlando Jose Tardencillas Espinosa, 19, caused a fiasco of potentially historic importance Friday when U.S. officials allowed him to talk with reporters in the belief he would support the administration's case. Instead, he recanted earlier confessions made in El Salvador, said they had been forced from him by torture and death threats, and denounced the U.S.-backed Salvadoran government as "criminal" and "fascist."

The administration, facing a fresh storm of questions about the credibility and wisdom of its actions, reacted by putting the maximum possible distance between itself and Tardencillas, who had been a prisoner in El Salvador since his capture by government forces there in January, 1981.

At approximately 3 a.m. yesterday, State Department officials turned him over to Nicaraguan Ambassador Francisco Fiallos; after a few hours' rest, embassy officials put Tardencillas aboard a commercial flight on the first leg of his journey to freedom in Nicaragua.

He left behind a situation that one department official privately described as "a state of turmoil" about what can be done now to get back on course with the administration's campaign to win public support for its Central America policy of portraying Cuba and Nicaragua as the agents of a communist threat to the Western Hemisphere.

The Tardencillas interview had been intended as an important element in a step-by-step drive, launched last week, to overcome escalating public and congressional concern that President Reagan is leading the United States into a Vietnam-type situation in El Salvador. The administration's aim is to convince the public that it has solid evidence to document its charges of communist interference in Central America posing a threat to U.S. interests.

But the official, who asked not to be identified, acknowledged that the misfire caused by the Tardencillas interview "has left us sufficiently shaken that we can't ignore the possibility of our credibility being at stake. Right now, we just don't know what we're going to do next."

"There is no predisposition to panic and cave in," he said. "We have so much stuff that we feel leaves absolutely no doubt about Cuban and Nicaraguan aid and direction for the Salvadoran guerrillas. But there are big problems about when to use it and how to use it."

He reiterated the contention, advanced repeatedly by Secretary of State Alexander M. Haig Jr. and other senior officials, that most of the administration's best evidence cannot be made public because it would compromise intelligence sources and damage Washington's ability to collect information in the future.

"Our problem is that we cannot and will not release this stuff," the official continued. "So we have to look for other material that we can give to the public and that will make the same case on which our policy judgments are based. Then, when you do put out information and it turns on you like that guerrilla interview, there's a real risk that your whole case, including the information that you can't make public, will be discredited."

His comments underscored what has been a frequent lament of policy makers in the national security area since 1961 when President Kennedy, relying on what turned out to be faulty intelligence advice, launched the aborted Bay of Pigs action against Cuba.

In the intervening years, situations such as the Vietnam war and the Watergate scandal have made Congress and the public increasingly unwilling to accept the word and actions of the intelligence community at face value. That has caused an increasing problem for officials who must rely on intelligence data to make policy decisions and who then find their efforts to justify these decisions hampered because they must keep much of the intelligence secret or because what they can make public often involves inconclusive information subject to differing interpretations.

President Carter learned that when his administration's charges about Cuban interference in the Shaba province of Zaire and the buildup of a Soviet brigade in Cuba encountered widespread skepticism about the validity of the intelligence on which they were based.

Under President Reagan, the problem has become even more acute because of his administration's stated intention to restore the influence and prestige of U.S. intelligence agencies. That, coupled with the administration's penchant for tough-sounding Cold War rhetoric, has subjected it to frequent criticism from its opponents that on some East-West issues--such as its charges that the Soviet Union and its allies have used chemical warfare in Afghanistan and Southeast Asia--its public assertions have gone further than seems justified by the publicly available intelligence.

That has been especially true of the controversy over the administration's contention that the Central America situation is part of a global communist conspiracy to win control of Third World areas.

Last year, when the administration made public a "white paper" intended to prove its charges of a massive flow of communist-supplied arms into El Salvador, it encountered a barrage of criticism that much of its information was inaccurate, ambiguous or insufficient to back up the charges.

Since then, an internal debate has raged sporadically within the administration about the wisdom of pursuing such efforts. On at least one occasion, plans for a second "white paper" were canceled after some officials cautioned that it would only rekindle arguments about accuracy.

Whether the damage to the administration's policies will be permanent is an open question. But its immediate effects were clearly to put the United States on the defensive and give Nicaragua an almost undreamed-of opportunity to score propaganda points in its dispute with the United States.

Fiallos, interviewed yesterday by the Cable News Network, repeated his government's charge that the United States has a "master plan" to pave the way for military intervention in his country.

Reports from Nicaragua said government officials there have started wringing the maximum possible propaganda advantage out of the situation, including having Tardencillas' mother make a tearful public plea for the safe release of her son.

Here at home, the State Department and news organizations have been blitzed by calls from Americans concerned about the prisoner's safety and questioning the legality of the government's action in bringing him here.