President Reagan pointed to the heart of his problem with many of his critics in his press conference Tuesday. These critics, many of them Democrats, are not listening to what the President says about the peaceful, or nonmilitary, side of his policy toward Central America. They are watching what he does rather than what he says, and suspect that no matter how much Reagan talks about peaceful solutions, his instincts could lead the nation toward war. Many fear a step-by-step, Vietnam-style involvement in a Central American quagmire.
''First of all, there is no comparison with Vietnam,'' said Reagan at the Tuesday press conference, answering a question about projected US military exercises in and around Central America. But he acknowledged that the American people might be confused by the suggestion being made in the press that somehow there is an ''ulterior purpose'' in the exercises. To many observers, the exercises look more than routine.
In his opening statement at the press conference, President Reagan accused his critics of paying too much attention to the military side of the policy and not nearly enough attention to the three other elements: support for economic development; dialogue and negotiations; and democracy, reform, and human freedom. Reagan said the planned military exercises in the Caribbean and Central America were training exercises and nothing more.
None of this seemed to appease Democratic critics, some of whom are convinced that behind the President's publicly proclaimed plans is a hidden agenda to overthrow the Sandinista leaders of Nicaragua. Despite Reagan's letter of support for the peace-seeking efforts of the Contadora group of four Latin American nations, the critics don't think the President is backing that effort in any wholehearted way.
The President's press conference came at a critical time for the administration, just two days before the House of Representatives was expected to vote on a bill aimed at halting secret funds for Nicaragua's anti-Sandinista guerrillas. While the President's press conference remarks apparently did little to calm his critics, there were enough Democratic congressmen seeking a ''middle way'' on the secret-funding vote to give the administration a chance at averting an aid cutoff.
Rep. Michael D. Barnes (D) of Maryland, chairman of the House subcommittee on hemispheric affairs, said that Reagan's press conference had done nothing to alleviate the concern of his colleagues about Central America and that, on the contrary, this concern was growing. He asserted that Latin American nations friendly to the United States had been taken by surprise by the US naval maneuvers now beginning off the Pacific coast of Central America.
''My sense of it is that we are making decisions on a day-to-day basis, and have not thought through the implications of some of the actions we're taking,'' Mr. Barnes said in a breakfast meeting with reporters.
Barnes said his guess was that policy was being run largely by William P. Clark, the President's national-security adviser, who does not have a strong background in Central American issues. Barnes also suggested there might be people in the administration who would like to see an incident develop, like the Tonkin Gulf incident of 1964 which led to the American bombing of North Vietnam. Such an incident, he said, could provide the excuse for military action against the Sandinistas.
Referring to reports of administration plans to increase secret funding for the anti-Sandinista guerrillas and thus provide for a force of 12,000 men, Barnes said: ''Twelve thousand men. That's not some minor operation. That's a war. The US is at war.
''There is no doubt in my mind that there are key people in the administration who believe we should support those who want to overthrow the government of Nicaragua,'' Barnes said.
Three former secretaries of state under Democratic administrations - Dean Rusk, Cyrus R. Vance, and Edmund S. Muskie - have, meanwhile, signed a statement opposing the use of secret funds to support the anti-Sandinista guerrillas.
Some of the critics are reluctant to back the administration because they believe that its declarations about the degree of Soviet and Cuban involvement in Central America are exaggerated. In his press conference, President Reagan asserted once again that ''the trouble that is going on down there . . . is revolution exported from the Soviet Union and Cuba and from others of their allies.'' He said that a Soviet freighter was at that moment approaching Nicaragua's main port of Corinto with a load of military equipment.
Reagan got support for his allegations of Soviet and Cuban involvement from a former Salvadorean guerrilla commander named Alejandro Montenegro.
Mr. Montenegro, who was captured late last year in Honduras and who is here under State Department sponsorship and protection, said in an interview that Vietnam had traumatized so many Americans that they were afraid to face the reality which confronted them in Central America. Montenegro said his guerrilla unit had received US-made weapons which were captured in Vietnam and then sent to El Salvador by the Soviet Union via Cuba and Nicaragua. EL SALVADOR * 55 US military advisers * 32,000 Salvadorean military troops and guardsmen * 4,000 to 7,000 guerrillas HONDURAS * 300 US military advisers and technicians * 4,000 US troops to be in US-Honduran military exercises * 8,000 anti-Sandinista rebels NICARAGUA * 2,200 Cuban, Soviet, and East bloc military advisers * 6,000 Cuban, Soviet, and East bloc 'civilian' advisers * 75,000 Nicaraguan Army troops and militiamen COSTA RICA * 2,000 anti-Sandinista rebels Source: US government