The non-Communist countries of South-east Asia are threatened by a "hostile challenge" from Indochina and must meet it by cooperating with one another and the major industrialized nations, leaders of the five pro-Western governments in the Association of Southeast Asian Nations said today.

As a two-day ASEAN conference opened, the leader, from Thailand, Malaysia, Singapore, Indonesia and the Philippines, completed draft joint statements seeking increased economic support from Japan, Australia and New Zealand, and improved trade relations with them.

Prime Ministers Takeo Fukuda of Japan, Malcolm Fraser of Australia and Robert Muldoon of New Zealand are to be here Sunday and Monday. According to an ASEAN source, the association does not expect Australia and New Zealand are to be here Sunday and Monday. According to an ASEAN source, the association does not expect Australia and New Zealand to agree to reduce tariffs on their commodity imports from ASEAN nations, but does expect Japan to commit $1 billion to finance five industrial projects, to remove or reduce tariffs, and to contribute to a fund to stabilize the prices of ASEAN exports.

While the emphasis of the conference will be economic, the ASEAN leaders have already taken note of the line drawn between Communist Indochina and the ASEAN countries since the end of the war in Vietnam, Laos and Cambodia.

Thai Prime Minister Thanin Kraivichien told the opening meeting at Kuala Lumpur's Hilton Hotel: "The general hostility displayed toward ASEAN as a collective entity by a neighboring country has given rise to a new situation country has given rise to a new situation facing this region. It is now evident that ASEAN is being challenged."

Thanin, a vociferous anti-Communist, has responded mildly to recent armed attacks by Cambodian troops on Thai territory. He suggested that the best way for the ASEAN countries to respond to an Indochinese challenge is to cooperate among themselves.

Philippines President Ferdinand Marcos said the ASEAN countries are strong enough "to eliminate the gaps that are supposed to exist" between them and Vietnam.

Marcos said he is "taking steps to eliminate one of the burdens of ASEAN" - the Philippines' claim to the Malaysian state of Sabah on the island of Borneo.

In recent weeks, the media of Vietnam and Loas, and of the Soviet Union, have stepped up their attacks on ASEAN, accusing it of being a military front for U.S. interst.

Singapore's Prime Minister Lee Kuan Yew dismissed such charges, saving that "Americans have shown how allergic they are to military involvement in any place in the world which does not directly threaten their strategic interest."

Nothing that ASEAN officials are to meet in Manila next month with senior State Department representatives, Lee said that while the United States wants to support ASEAN'S development, "Their only major strategic consideration in Asia is Japan."

Lee, who is regarded as a tough-minded pragmatist, urged his colleagues to reach quick agreement on "concrete items, the bolts and nuts of economic cooperation," so as to be take seriously by the United States and other industrialised nations.

It is clear from what Lee and other leaders said that ASEAN will try to persuade Japan to step into the region as a kind of economic substitute for the United States, whose interest has waned since the end of the war in Indochina.

Some diplomatic observers here believe that President Carter has pressed Fukuda to step up Japan's economic and political activity in Southeast Asia, and Japan seems interested in becoming more deeply involved both in ASEAN countries and in Communist states, particularly Vietnam.

A number of ministers have indicated that Japan is prepared to make substantial investments, but that the ASEAN nations do not seem ready to make the best use of the funds.

Malaysia's trade and industry minister, Hamzah Abu Samah, siad that feasibility studies on the five projects Japan has agreed to consider have not been completed, and that three have not been started. The projects are a diesel engine plan in Singapore and fertilizer factories in Malaysia, Indonesia, Thailand and the Philippines.