Henry A. Kissinger was completely out of character yesterday, avoiding reporters seeking out his intentions as President Reagan's appointee to head the new commission on Central America's military, political, economic and social turmoil.

Since the start of the Reagan administration, there had been speculation that the irrepressible Kissinger would emerge in some prominent administration post, over opposition of the Republican Party's extreme right wing.

When asked to head the commission, Kissinger was surprised and extremely skeptical, and not because of false modesty, according to associates. That is never the issue in Kissinger's moves.

Instead, his doubts apparently centered on whether he would become enmeshed in a hopeless cause, they said, and for Kissinger that is exceptionally important. No other former secretary of state or national security affairs adviser has managed to remain as long at or near the center of the world stage, lauded by admirers, excoriated by critics and, above all, unforgotten.

Conflicts in Nicaragua and El Salvador are not issues on which Kissinger has made public claim to expertise, nor do they evoke the high drama of great power clashes on which the Kissinger legend has been built. "I think it's a very unenviable job," one Kissinger associate said yesterday, adding, "unenviable, if not hopeless."

Kissinger's close friends can always be counted on to make supportive statements, maximizing obstacles that he must surmount. But in this case, one source said, Kissinger was deeply uncertain what to do about the commission post.

"He was very negative about it, and they put a lot of pressure on him," the source said.

Kissinger's prestige has been pounded recently by new controversy aroused by author Seymour M. Hersh in his book, "The Price of Power: Kissinger in the Nixon White House." Kissinger was almost apoplectic in challenging what Hersh set out as unending manipulations and duplicities by Kissinger.

The appointment demonstrates, nevertheless, that Kissinger's name still carries enough prestige to interest the Reagan administration, despite denunciation on the right flank. At a news conference yesterday, Richard A. Viguerie, publisher of Conservative Digest, said, "It would be difficult to find a spokesman less trusted by liberal and conservatives than Dr. Kissinger."

Kissinger backers, however, said they found it ironic that for the second time the Reagan administration has called in principal foreign policy advisers who served the President Ford to help salvage foundering policy. Brent Scowcroft, national security affairs adviser to Ford when Kissinger was secretary of state, heads the continuing presidential Commission on Strategic Forces, and Kissinger served as a counselor to the panel in its earlier advice on MX missile deployment. Kissinger now is chairman and Scowcroft vice chairman of the international consulting firm of Kissinger Associates.

Central America was never a major focus of Kissinger's diplomacy, except for talks on the Panama Canal treaties, which Reagan strongly opposed. The administration presumably wants from him now not details but support and justification for its policies in a convincing global context. This can be a formidable test for Kissinger, for it can also generate renewed controversy about his diplomacy in Indochina and Chile.