Speaking separately but in a public show of near harmony, the Carter administration's two principal advisers in foreign policy matters yesterday sought to defend President Carter's record against the rising clamor of criticism on the right.

Secretary of State Cyrus R. Vance voiced concern about "the distorted proposition being advanced by some that America is in a period of decline." This view, he said without naming names, "is not only wrong . . .but dangerous as a basis for policy."

Zbigniew Brzezinski, the president's assistant for national security affairs, spoke of Carter's success in enhancing "American historical confidence by infusing a higher degree of moral commitment into our policy."

Both speeches were vigorously flogged on the Washington media circuits by aides to both officials as major pronouncements. Despite the differences of doctrine or approach ascribed to Vance and Brzezinski on other occasions, the messages were described as "complementary." The two men had read and approved one another's statements prior to delivery.

Vance, though not identifying the targets of his criticism, could well have been referring to opponents of the strateic arms limitation treaty (SALT) who take a more alarmed view of Soviet power and intentions than that of the administration.

"We would imperil our future if we lost confidence in ourselves and in our strength, and retreated from energetic leadership in the world," Vance said. "And we would imperil our future, as well, if we reacted in frustration and used our power to resist change in the world, or employed our military power when it would do more harm than good."

Brzezinski also spoke of acceptance of global change as a keystone of the president's foreign policy. "Any attempt to create artificial obstacles to change for the sake of the status quo will merely foster U.S. isolation and irrelevance," he said.

As in most speeches produced by a bureaucratic committee process, the words were couched in cautious abstractions. Whatever differnces may simmer between the two officials on substantive issues were barely hinted at in their respective drafts.

Brzezinski, after enumerating the foreign policy achievements of the Carter administration, reiterated his concern about "the arc of crisis that stretches across southern Asia to southern Africa . . .countries whose internal difficulties make them vulnerable to external exploitation."

Vance, on the other hand, said the administration "will oppose attempts by others to transform local disputes into international tests of will." He spoke for a policy of "healing, rather than fueling, local conflicts."

This is a question of foreign policy approach on which the two men have been pronounced to have been in sharpest divergence, though they have publicly denied it. Brzezinski spoke last night before an audience of the media elite, the American Socety of Newspaper Editors, at the New York Hilton. Vance's audience was the American Association of Community and Junior Colleges at the Conrad Hilton in Chicago.