According to recent polls, most Americans are concerned about Central America, U.S. policy and the threat of communist expansion there. At the same time, the vast majority have only the vaguest idea which countries are which, whose side we are on and why the various factions are fighting each other.

The Reagan administration complains that the reason its policies have met with so much domestic opposition is that the media has done a poor job of explaining the situation. The administration recently organized its own "truth squad" and ordered top level officials to begin spreading the word that Central America is important to us and communism must be stopped there.

But if the media has fallen down on its task of informing the American people, it has not been for lack of trying. For nearly four years now, one war or another in Central America has been front page news, and the television networks have entered into a seemingly endless competition with documentaries that pose, and then purport to answer the questions of who is winning, who is losing and who cares.

Tonight's contribution to the sum of information on Central America is "NBC Reports: Central America . . . Summer of Decision" on Channel 4 at 10. The program doesn't really explain why this summer is different from any other, except to state that Central America is undergoing political and social turmoil "unlike any other in its history," a debatable assumption, considering the 150 years of nearly continuous wars, coups and uprisings the region has been through.

Presumably, the current crux of the matter is the threatened congressional limit on funds available to the administration after the end of the fiscal year in September to fight leftist guerrillas in El Salvador and to stem the power and influence of Nicaragua's leftist government.

According to producer Bob Rogers, quoted in a network handout, "This program won't solve the problems nor will it magically educate all viewers in the geography of our southern neighbors. But it will go a long way toward informing Americans on the background and the issues and options in what may be the most important debate this side of nuclear disarmament."

Unfortunately, "Summer of Decision" goes only about as far as the Reagan administration in explaining Central America and the problems it poses for decisionmakers here. Most of the program, with NBC correspondents Robin Lloyd and Richard Valeriani, is devoted to Nicaragua and what its critics have to say about the ruling Sandinista National Liberation Front. They include priests, businessmen, a small farmer, a journalist, anti-Sandinista guerrillas of various persuasions, several State Department-supplied defectors and Secretary of State George Shultz, among others.

"For many Nicaraguans," the narration goes on to say, "this revolution is worth dying for." Yet except for a cursory bow to Sandinista health and education programs, the only Nicaraguan shown having anything remotely positive to say about it in a fairly unrelentingly negative presentation is Interior Minister Tomas Borge, hardly your average Nicaraguan.

Honduras is given a light once-over and a few minutes are devoted to "increasingly aggressive," Nicaraguan-aided Salvadoran guerrillas fighting a local army that has a "leadership" crisis. Little or nothing is said about the human rights problems, the killing of American citizens, the military corruption or the political terrorism that form the basis for the debate over U.S. participation in El Salvador.