A sizable majority of Americans sees entanglement in the problems of Central America as a greater danger to the United States than the spread of communism there, according to a Washington Post-ABC News public opinion poll.

Most citizens, including many who are otherwise strong supporters of President Reagan, said that they sharply oppose any increase in U.S. involvement in the struggles in Central America. By more than 3 to 1, for example, they reject Reagan's proposed increase in U.S. military aid to the government of El Salvador for its fight against leftist guerrillas.

Although a majority accepts Reagan's argument that Central American problems "directly affect the security and well-being of our own people," only 3 of every 10 people polled say they believe they pose a serious threat to the United States.

A broad consensus of more than 80 percent also accepts Reagan's view that a rebel victory in El Salvador could destabilize the entire region and that the Soviet Union, Cuba and Nicaragua are working to accomplish that end. But, by a ratio of more than 2 to 1, the public says that it feels "poverty and the lack of human rights" are a greater cause of unrest in Central America than is subversion by those nations. By an even greater margin, 6 to 1, the Americans polled say that they oppose any secret attempt to overthrow the leftist Sandinista government of Nicaragua, regardless of its support for the leftist rebels in nearby El Salvador. Contress is currently considering whether to cut off covert Reagan administration aid to Nicaraguan guerrillas trying to topple the Sandinistas.

Many citizens are skeptical of declarations by Reagan and other officials that the administration has no intention of sending U.S. combat troops to El Salvador, according to the poll. While 46 percent say that they believe such administration statements, 40 percent say that they do not and 14 percent express no opinion.

By more than 2 to 1 in the poll, citizens said they believe Reagan would seek to send troops to El Salvador if the government there cannot defeat the leftist rebels. But they oppose such a move, even as a last resort, by an almost 6-to-1 margin.

In his televised address before a joint session of Congress on April 27, Reagan said that "the national security of all the Americas is at stake in Central America" and that the government of El Salvador "is under attack by guerrillas dedicated to the same philosophy that prevails in Nicaragua, Cuba, and, yes, the Soviet Union."

The Post-ABC News poll, in a survey of 1,501 people May 11 through 15, asked:

"Which would you say is a greater danger to the United States: the spread of communism in Central America because the U.S. doesn't do enough to stop it, or the U.S. becoming too entangled in internal Central American problems as a result of trying to stop the spread of communism?"

Fifty-five percent answered that entanglement is the greater danger. That sentiment was expressed in about equal degree in all regions of the country; it was especially pronounced among women and prevailed among a majority of men. Meanwhile, 34 percent said that the spread of communism is the greater danger, and 11 percent offered no opinion.

Another question asked whether the United States "should secretly try to overthrow the government of Nicaragua, or not." Thirteen percent favored such covert action and 78 percent opposed it, with 9 percent expressing no opinion.

Asked whether they felt the United States "has been trying to secretly overthrow" the Sandinistas, 32 percent said "yes," 41 percent said "no" and 27 percent expressed no opinion.

In a March, 1982, Washington Post-ABC News survey, 21 percent said that they felt the United States should help the Salvadoran government, 2 percent wanted the United States to help the rebels and 68 percent said the United States should stay out of the situation. Now, 15 percent want the United States to support the government, 3 percent the rebels and 69 percent want the United States to stay out altogether.

In 1982, 21 percent approved and 72 percent disapproved of sending additional military equipment and weapons to the Salvadoran government. Now, 19 percent approve and 70 percent disapprove.

In both surveys, many of those interviewed showed a lack of knowledge, with only 65 percent in 1982 and 55 percent now able to say it is the Salvadoran government, not the rebels, that the United States is supporting. In only a few areas are there sharp differences in attitudes between those who know this and those who don't, however.