Secretary of State Alexander M. Haig Jr. told the foreign ministers of non-communist Asia here today that the United States will not normalize its relations with Vietnam or ease its economic and political pressures as long as Vietnamese troops occupy Cambodia.

Spelling out a tough U.S. policy toward Vietnam, Haig also called for more concerted international political, diplomatic and economic efforts to deal with the Vietnamese refugee problem "at its source."

Haig did not refer to military pressures on Vietnam, a subject mentioned publicly in Peking this week by Assistant Secretary of State John H. Holdridge.

Under questioning in a news conference here, Haig said no decision has been made to provide U.S. military assistance to a noncommunist "third force" to oppose the Vietnamese in Cambodia.

He told the annual foreign ministers meeting of the Association of Southeast Asian Nations (ASEAN) that the United States will give strong backing to the planned international conference on Cambodia at the United Nations starting July 13.

The strategy for that conference and follow-on aspects of Cambodia-related pressure on Vietnam was the focus of the talks among Asian diplomats here. In a statement that caused some irritation when it was made public, Japanese Foreign Minister Sunao Sonoda disclosed details of a comprehensive Japanese plan on Cambodia that Southeast Asians said was very close to one they have been considering in secret.

"The Japanese are stealing our show," one ASEAN diplomat complained.

Japan, the United States and other countries regularly attend meetings of the foreign ministers of the five ASEAN countries -- Thailand, Indonesia, Malaysia, Singapore and the Phillippines.

Since the Vietnamese invasion of Cambodia 2 1/2 years ago, U.S. policymakers have relied on a combination of political pressures mounted by Southeast Asian nations and military pressures of China to contain Hanoi's activity.

The repercussions of the U.S. defeat and withdrawal from Vietnam, referred to today by the conference chairman, Philippine Foreign Minister Carlos P. Romulo, as "scars not only on the American people but on all of us," seemed almost to preclude renewed U.S. military involvement in Indochina.

Haig's strong attacks on Vietnam, which he accused of imposing "thinly disguised vassalage" on its neighbors, were reminiscent of the earlier era. Under questioning, however, Haig said that "recourse to [U.S.] military action is not a normal or anticipated approach to the problem."

The planned U.S. arms relationship with China, made pulbic by Haig Tuesday in Peking, may bring indirect U.S. military pressures to bear in Cambodia. Haig discussed the U.S. arms sales shift in low-key fashion here, describing it to ASEAN ministers as "an internal decision in the U.S. bureaucracy" that merely involved shifting China from one "category" to another on arms sales.

Regarding ecnomic pressures that the United states is mounting against Vietnam in international aid deliberations, Haig said, "we will continue to question seriously any economic assistance to Vietnam -- whatever the source -- so long as Vietnam continues to squander its scarce resources for aggressive purposes."

In the superpower dimension, Haig charged that "there has been the intrusion into the region of a Soviet military presence in the form of operating facilities at Cam Ranh Bay and elsewhere in Vietnam and increased military activity in the waters and air space of the western Pacific and Southeast Asia."

In response, he pledged, "The United States will maintain and strengthen its own military capability in the Pacific and Asia as a contribution to the security of the area in the face of the Soviet military buildup." Haig flew later in the day from Manila to Wellington, New Zealand, where he will attend a meeting of the security alliance grouping New Zealand, Australia and the United States.

In its communique Thursday, ASEAN urged Vietnam to join efforts to reach a "comprehensive political settlement" in Cambodia, where 200,000 Vietnamese occupation troops have been propping up a government installed by Hanoi in 1979.

Among the initial steps toward such a settlement, ASEAN listed the dispatch of a U.N. peacekeeping force to Cambodia, the withdrawal of all foreign armed forces "in the shortest possible time" under U.N. supervision and the disarming of all Cambodian factions immediately after such a pullout.

Communist Khmer Rouge guerrillas, led by ousted Cambodian dictator Pol Pot, have been battling Vietnamese forces for the past 2 1/2 years. In the past, Pol Pot has rejected proposals by noncommunist Cambodian resistance groups that Khmer Rouge forces be disarmed as part of a settlement.

A major complication in Western and ASEAN efforts to promote a settlement is ensuring that the Khmer Rouge regime, considered one of the most brutal in modern history, will not return to power.

Currently, however, a majority of the United Nations, including the United States, China and ASEAN, continues to recognize the Khmer Rouge as Cambodia's government.

ASEAN and its Western supporters have been encouraging creation of a united front of Khmer Rouge and noncommunist Cambodian resistance groups with the participation of former Cambodian head of state Prince Norodom Sihanouk and former prime minister Son Sann.