The Reagan administration took a wary stance yesterday toward the new military rulers of Guatemala amid reports of new developments in the volatile Central American situation.

The State Department withheld substantial comment on the Guatemalan coup while seeking a clearer picture of the new regime's likely political direction.

Officials at State and at the White House also refused to comment on a report by CBS News that Gen. Vernon Walters, ambassador at large and veteran secret emissary, visited Cuba earlier this month in an effort to persuade President Fidel Castro to drop support of Central American guerrilla movements.

Secretary of State Alexander M. Haig Jr. and other State Department officials have said in recent days that they anticipate direct talks between the United States and Cuba, and the United States and Nicaragua, to begin sometime after this Sunday's elections in El Salvador. No details have been announced.

While refusing public confirmation, administration officials acknowledged privately that Mexican Foreign Minister Jorge Castaneda was correct when he said yesterday that representatives of the United States and Nicaragua probably will meet soon in Mexico City.

These officials said the United States is unlikely to respond publicly until after Sunday's Salvadoran elections for a constituent assembly. But, they added, the administration--while skeptical about the chances for progress--is committed to the talks and tentatively expects to send Thomas O. Enders, assistant secretary of state for inter-American affairs, to Mexico for an exploratory round after the election.

Regarding the Guatemalan coup, State Department officials said privately that they have no sense of whether the military group that ousted President Romeo Lucas Garcia Tuesday is sincere in its professed dedication to reform and democratization or whether it represents a continuation, in another guise, of rule by rightist military and business forces that traditionally have dominated Guatemala.

Until that question is answered, the officials stressed, there is no way to tell whether events there might offer the administration an opening to pursue the closer military relationship it believes essential to countering communist penetration of Central America.

Haig and other officials suggested that Guatemala may be the next "domino" in a bid to subvert Central America through campaigns of guerrilla warfare and terrorism. They also have made no secret of their belief that the United States has a vital interest in helping the Guatemalan armed forces turn back this threat.

But Haig also has conceded that there is little hope of resuming severed ties with the Guatemalan military until authorities there take steps to end rights abuses and authoritarianism that have prompted Congress to block renewed security assistance.

Administration officials originally hoped to find an opportunity for a fresh start in the Guatemalan presidential elections earlier this month. But that hope was dashed by charges of fraud and manipulation by the military that arose after the balloting and that led finally to Tuesday's coup.

Last night, the administration still was pondering whether the takeover by a junta led by retired Gen. Efrain Rios Montt might offer another chance to prod Guatemala toward a moderate course acceptable to Congress.

But, as one official said, "It's too early to be optimistic or pessimistic. There are just too many questions to which we don't yet have answers."

Some officials acknowledged that reports from the U.S. Embassy in Guatemala City are not reassuring.

The officials said the embassy, while initially encouraged by the apparent reformist bent of younger officers who led the coup, subsequently warned that emergence of Montt and others in the group that now appears in command might be a sign that power has reverted to traditionalists dominating the Guatemalan power structure.

There has been considerable speculation here and in Guatemala that the coup was intended not to nudge the country toward reform but to overcome the bad odor left by the elections and permit Washington to resume aid by disguising continued control of the military and its allies under a new facade.

The State Department also announced that the foreign ministers of El Salvador, Honduras and Costa Rica, which recently formed a Central American Democratic Community, will meet here today with President Reagan and Haig to discuss the administation's Caribbean basin initiative and other issues affecting the region.