Secretary of State Alexander M. Haig Jr. called on the nations of the hemisphere today to take collective action against what he described as threats to peace and security from Cuba and Nicaragua.

Speaking to the general assembly of the Organization of American States, Haig described rising dangers of "terror and war in the region" but did not propose specific actions that the OAS or its member nations might take in response.

Haig mentioned the hemisphere's 1947 Rio Treaty of collective security but did not propose that it be invoked at this point against Cuba or Nicaragua.

A senior aide to Haig on Latin American matters, in a briefing for reporters, said the address was aimed at "starting a process" and "launching a concept" that might lead in time to collective action. The official forecast follow-up meetings to include some but not all 27 of the OAS member states.

Another State Department official said "joint contingency planning" by the United States and some of its hemispheric allies could be one aim of forthcoming meetings.

Haig's address, together with his discussions with senior Latin American diplomats here in the past two days, suggested an administration decision to mute the talk of unilateral U.S. military steps in Central America and to shift attention to regional responsibility and solutions.

Nicaraguan Foreign Minister Miguel D'Escoto immediately challenged Haig's charge that his country is intervening militarily in El Salvador by aiding guerrilla forces there. D'Escoto charged in a press conference following Haig's speech that Washington, rather than Managua, "is clearly violating the principle of nonintervention" in Central America and elsewhere.

The consensus of comments by Latin diplomats to Haig's address appeared to be positive. But it was unclear how many hemispheric nations would be willing to participate in military steps to combat Cuban or Nicaraguan activity.

"The United States is prepared to join others in doing whatever is prudent and necessary to prevent any country in Central America from becoming the platform of terror and war in the region," Haig said.

Haig declared that "President Reagan has made clear that we have no plans to send combat troops to Central America" but he also said the United States will help hemispheric nations resist "illegal intervention" and will supply economic and military assistance when needed.

Haig asked: "Should we not be discussing together how to prevent the import of heavy offensive weapons -- by any country in Central America? Should we not be searching for ways to limit the number of foreign military advisers to reasonable levels -- in all countries of Central America?"

The secretary of state left no doubt he was asking the questions about Nicaragua, where he said "pluralism is in danger of repression" and "the possibility of economic progress...is being undermined by militarization."

Under the Sandinista regime, Haig charged, Nicaragua is "working to establish" the largest military force in Central American history, with the aid of at least 1,500 Cuban military and security advisers.

Haig also charged: "Nicaragua's arsenal already includes tanks and other heavy offensive weapons never deployed before in Central America. Pilots are being trained and facilities readied for modern jet fighters.

"Meanwhile, the principle of nonintervention is being violated as arms, ammunition and other military supplies flow from Nicaragua to the Salvadoran insurgents." A possible upshot of this is "a costly arms race at the expense of economic development and social progress," Haig declared. He went on to express the possibility, attributing it to a "fear" by other nearby nations, that "the militarization of Nicaraguans is but a prelude to a widening war in Central America."

Haig's senior aide reiterated U.S. evidence of preparations in Nicaragua to receive Soviet-built Mig fighters and said that, despite D'Escoto's assurances to Haig two days ago, it is "a fair presumption" that the warplanes are on the way. Another high U.S. official confirmed that D'Escoto will soon visit Moscow for talks with Soviet officials.

Speaking of U.S. proposals to Nicaragua made several months ago by Assistant Secretary of State Thomas O. Enders, his top aide on Latin matters, Haig told the OAS meeting, "If Nicaragua addresses our concerns about interventionism and militarization, we are prepared to address their concerns."

Haig added, "We do not close the door to the search for proper relations." His senior aide said, however, that Nicaragua had sent a letter to Washington saying "they rejected our proposals" and that D'Escoto presented "nothing new" on this subject to Haig in their meeting here Wednesday.

The Nicaraguan foreign minister, in a news conference, gave a different account. He said the United States made two written proposals: to enforce the U.S. laws on neutrality, thus curbing activity of Nicaraguan exile groups conducting paramilitary training on American soil, and to issue a joint statement foreclosing threats or use of force.

D'Escoto said, "We didn't reject this" but asked in reply for U.S. actions in line with these proposals as a next step. He said Nicaragua's Oct. 31 message to Washington, which he described as the last written communication on the subject, had not been answered.

In addition to discussing Nicaragua, Haig charged that "since 1978, Cuba, with the support of the Soviet Union, has embarked on a systematic campaign of increasing interference against its neighbors."

Haig added: "Havana calls the leaders of violent opposition groups together, forges unity pacts among them, trains their men, provides their arms and sends them back to mount a violent challenge to legitimate governments." He said this is taking place in El Salvador, Guatemala and now Colombia.

Haig devoted a large part of his speech to economic problems, saying "bold action" is necessary to reverse the serious economic decline of many countries in the region.

The secretary of state spoke in slightly more concrete terms than previously about the Reagan administration's proposed "Caribbean basin" program. He said it could include unprecedented free-trade arrangements in the U.S. market. Aides said it now appears the program will not be ready to be unveiled until next year.