Secretary of State Cyrus R. Vance yesterday outlined a U.S. policy approach to Latin America emphasizing both vilgilance against "outside interference" in the hemisphere and cooperation with internal pressure for radical changes such as those currently taking place in Nicaragua.

In a speech to the Foreign Policy Association in New York, Vance sought to draw a distinction between the two situations that have thrust Latin America back into the forefront of U.S. foreign policy concerns.

These involve Cuba, where the Carter administration is involved in a potential confrontation with Moscow over the deployment with Moscow over the deployment of Soviet troops, and Nicaragua, where the administration has made the controversial decision to seek friendly ties with the radical Sandinista-dominated government that seized power there in July.

Because of the Cuba controversy's implications for U.S.-Soviet relations on a global scale, Vance's assertion that "we will assure that our interests are fully protected" was the part of his speech that drew the biggest share of attention.

But, U.S. officials said privately, of equal importance to an understanding of the policy implications of his speech was his focus on Nicaragua. In that context, Vance said:

"By extending our friendship and economic assistance, we enhance the prospects for democracy in Nicaragua. We cannot guarantee that democracy will take hold there. But if we turn our backs on Nicaragua, we can almost guarantee that democracy will fail."

These words, the officials said, were intended to signal the administration's determination not to fall back on the traditional attitude that the safest way to protect U.S. interests in Latin America is through close identification with rightist military regimes with strong anti-communist attitudes.

Nicaragua, where for almost four decades the United States strongly supported the Somoza family dictatorship, overthrown by the Sandinistas, was the most obvious example of that policy. In reference to that, Vance said:

"It may take time for us to overcome the legacy of the past and to develop a relationship of mutual trust with the new government. We must be patient, steady and prepared for inevitable disagreements. But so long as pluralism flourishes in Nicaragua -- and we respect it -- I am confident that relations will prosper."

He then sought to extend this policy to the rest of the region, where many countries continue to teeter back and forth between democracy and dictatorship.

He said, "Elsewhere in the region, we will encourage and support constructive change before the ties between government and people irreversibly erode and radicalism or repression drive out moderate solutions."

But, he added, "We must keep alive in our minds the important distinction between the social and political changes that result from internal factors, and those that result from outside pressures and forces.

"We must recognize that disruption within nations does not necessarily mean there is an outside hand. But at the same time, we must be alert to the the reality that internal tensions present opportunities for outside interference."

Then, taking aim at Fidel Castro's Cuban regime and its close ties with Moscow, Vance said, It is in this context that we have in the past expressed concern over Cuba's efforts to exploit for its own advantage social and political change within its neighbors . . . Cubs's ability to exploit these internal tensions is reinforced by its close military ties with the Soviet Union."

His remarks, which U.S. officials said were intended as a major statement of policy, came against a background of increasing high-priority attention within the administration for relations with Latin America.

In addition to the situations involving Cuba and Nicaragua, Vance and other top-ranking administration officals have been concerned by signs of increasing instability elsewhere in Central America and in the Caribbean and by the need to improve U.S. relations with such emerging hemispheric powers as Mexico, with its newly discovered oil wealth.

As a result, after a long period of relative inattention to hemispheric affairs, the administration has shifted into a whirl of initatives that in the next few days alone will see a state visit to Washington by Mexican President Jose Lopez Portillo and a trip by Vance and Vice President Mondale to Panama for ceremonies marking the first stage of transfer of the Anama Canal to Panamanian sovereignty.

It was largely to underscore these initatives, U.S. sources said, that Vance sized the opportunity of his speech yesterday to focus on Latin America and to restate the administration's determination to encourage and support those governments that respond to internal pressures for greater social justice and economic improvement for their people.

In short, the sources added, the thrust of Vance's message was that, while the United States will oppose efforts by Cuba or the Soviet Union to exploit these changes, it also will work closely with any herispheric country that couples its striving for change with respect for human rights and pluralism, even if these countries opt for political or eoconomic systems whose workings could cause friction with the United States.