President Carter has picked a highly experienced team fo three major Asian diplomatic posts - former Senate Majority Leader Mike Mansfield as ambassador to Japan, former Princeton University President Robert Goheen as ambassador to India and former State Departmet politico-military affairs chief Gorge S. Vest as ambassador to Pakistan.

Informed sources said last night the names of these are in the early stages of the necessary political, diplomatic and security clearances prior to public announcement and formal appointment by Carter.

All three men have impressive credentials for their future jobs. Japan is the senior U.S. ally in Asia, and U.S. relations with India and Pakistan are undergoing important changes.

Mansfield, 74, who retired in January after 34 years in Congress, was a professor of Far Eastern history at the University of Montana before coming to Washington and was deeply interested in Asian affairs during his Senate career. Earlier this month he flew to Hanoi as a member of Carter's mission on the missing in action from the Vietnam war.

Mansfield has visited Japan many times, the most recent trip having been this past summer, after which the former head of the Senate Foreign Relations Committee called U.S. Japanese relations "a fundamental pillar in present U.S. foreign policy whose goal is continued stability in the Western Pacific. "Japan, Mansfield said in a report on his trip, is a "cornerstone in that policy.

In his recommendations for the Carter administrations' policy toward its Pacific ally, Mansfield urged that there be no more "shocks," a reference to abrupt Nixon-Kissinger actions that affected Japan but which were taken without consultations. He also recommended continued reductions in the U.S. military presence in Japan and a "code of conduct for international commercial dealings which would outlaw practices such as those involved in the Lockheed affairs."

Goheen, 57, was born in India and lived the first 14 years of his life there while his parents served as medical missionaries. His selection to go to New Delhi comes at a time when Washington is reassessing its policies toward the subcontinent after the fall of Indira Gandhi's government that has indicated it intends to move away from India 's recent very close ties to the Soviet Union.

Goheen served as president of Princeton from 1957 to 1972.

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Vest, 58, a career diplomat, was chief U.S. representatives to the semi-secret London conference of nuclear suppliers during the Ford administration. Thus he is intimately familiar with the nuclear policy issues that are among the most pressing and delicate matters between the United States and Pakistan.

Relations between the two countries have been strained over U.S. opposition to Pakistan's planned acquisition from Franc of a nuclear fuel reprocessing plant capable of manufacturing atom bomb material. New talks between the two countries about the transaction are expected to begin soon.

Vest joined the State Department just after World II and has spent most of his career dealing with European affairs and with political-military questions. He was reported to be one of three persons under final consideration for ambassador to Israel, a position that went to another career diplomat, Samuel W. Lewis.