Southeast Asian foreign ministers called on the United States yesterday not to abandon the noncommunist countries of the region despite the traumatic experience of military defeat in Indochina.

In the first day of a two-day conference of top U.S. officials and the five-nation Association of Southeast Asian Nations (ASEAN), both sides took care to emphasize economic rather than military ties and involvement. The Asian ministers were explicit and outspoken in asking that the United States step up its trade, investment and political interest in the region.

"As an acknowledged leader on a global scale, and bication by the United States of its responsibilities in our region would almost certainly lead to a crisis of confidence at a time when mutual confidence is most needed," said Philippine Foreign Minister Carlos P. Romolo.

Singapore Foreign Minister Sinnathamby Rajaratnam, saying that the ASEAN countries remain "on your side" while much of East Asia "has gone to the other side," called for new help to the region in keeping with U.S. global interests.

He said the United States had appealed to Asian countries for many years to seek trade rather than aid. But now, he said, those who followed this advice are being confronted with opposition to the entry of their products here on grounds that this is "unfair competition" because of the law wages of Asian workers.

Several of the ministers made the point that the fall of Indochina three years ago brought about a greater degree of cooperation and cohersion among the remaining noncommunist states of Southeast Asia, and that these countries are doing better economically than their divided and still wartorn communist neighbors.

The United States, said Rajaratnam, now has a second chance in Southeast Asia "to prove what it failed to do the first time in Indochina - that the non-communist way can provide effective answers to the problems of Third World countries." He said this time the venture will require no U.S. troops but "the will and the imagination and a fraction of the money expended in Indochina."

Secretary of State Cyrus R. Vance, chairman of the U.S. delegation, reiterated U.S. pledges of general cooperation with ASEAN but gave no commitments to the specific tariff, trade and investment arrangements being sought by the group. "We want to help - not intervene," Vance said.

Vance spoke during a closed session of his support for an international "common fund" to stabilize commodity prices, an objective of ASEAN and other developing countries. However, implementation of the idea has been blocked by Treasury Department opposition.

Under questioning from Asian ministers, Vance said the United States has not been told by Vietnam "directly" that the previous conditions for establishment of diplomatic relations with Washington have been dropped, and so the Carter administration as yet has no response. In recent public statements and private remarks to Asian and U.S. diplomats, senior Vietnamese officials have indicated that American agreement to supply reconstruction aid is no longer required in advance of normalization of relations.

Eighteen persons representing a coalition of church and human rights groups picketed the National Press Club during a luncheon for the Asian ministers. Placards protested imprisonment and abuse of dissident leaders in several of the countries and charged that ASEAN is "a grouping of dictatorships."

Romolo, responding to a question at the press club luncheon, said "freedom and want" takes priority over "freedom of expression" in developing countries where living standards are still low.