Malaysia came under intense international pressure yesterday to reconsider its decision to expel the 76,000 Vietnamese refugees it has been harboring and to fire on any boats trying to bring more refugees to its shores.

U.N. Secretary General Kurt Waldheim called on Malaysia to "continue to provide temporary asylum for the refugees while international efforts to secure settlement places for permanent asylum are being pursued."

Poul Hartling, the U.N. high commissioner for refugees arrive, whose difficulties I well understand, respond in a manner that prevents appalling human tragedy."

Hartling urged the international community to double the 300,000 spaces now available for resettlement of the refugees.

Several countries, including the United States, expressed deep concern over the Malaysian decision while pressing the government in Kuala Lumpur for what were called "clarification" of the news reports about the Malaysians' new tough policy.

There seemed to be a growing consensus that there will be no solution to the flood of Indochinese refugees without unified effort on the part of the world community.

The United States has endorsed a call by Britain that a special conference be convened to take up the question. So far there have been three meetings of those countries most directly involved with the refugee issue but, in the opinion of those Asian countries that have been inundated with Indochinese fleeing their homelands, the results have been inadequate.

When he announced Malaysia's new tough policy on Friday, Deputy Prime Minister Mahatir Mohamad said the reason was that "third countries are not accepting as many refugees as are coming in."

Report from Tokyo quoted Japanese Foreign Ministry sources as saying that country intended to raise the question of an international conference at a meeting of nine nations, including the United States, scheduled for the Indonesian island of Bali July 2 and 3. According to the sources, the Japanese proposal calls for invitations to the meeting be sent to the Soviet Union, China and Vietnam.

Last week Secretary of State Cyrus Vance said that President Carter would take up the refugee question with Soviet President Leonid Brezhnev at the summit talks now under way in Vienna. Presumably Brezhev will be asked to exert pressure on Vietnam to stem the exodus of its people.

The Chinese Foreign Ministry issued a denunciation of Vietnamese leaders, calling them "the biggest and most despicable present-day human traffickers." Since 1975 Vietnam and China have been quarreling with increasing bitterness. At the root of their dispite is Hanoi's close ties with the Soviet Union.