The Association of Southeast Asian Nations renewed its policy of conciliation toward Indochina today, despite apparent doubts among some of the five member governments about the Communists' intentions in the region.

In a communique issued at the end of a two-day meeting of heads of governments, the five nations "emphasized the desire fo ASEAN countries to develop peaceful and mutually beneficial relations with all countries in the region, including Kampuchea [Cambodia] Laos and Thailand."

The communique coincided with a broadcast from Cambodia predicted that ASEAN is "doomed to failure" because of continuing differences among its members. Observers here said they believe that this was the first time Cambodia has made any comment about the association. Vietnam has repeatedly attacked ASEAN as an alleged military front for U.S. interests in Southeast Asia.

Differences among the member governments were clearly reflected in comments by several leaders. in a closing statement, Singapore's Prime Minister Lee Kuan Yew said the meeting "made us realize why certain objectives of ASEAN cannot be achieved as quickly as some of us would have wished them to be. There are difficulties which, for a variety of reasons, cannot be overcome as simply as we would wish."

Lee was referring , for the most part, to differences over a variety of industrial and trade-development projects, but in a press conference held by the five foreign ministers tonight further differences emerged over ASEAN's policies toward Indochina, and Vietnam in particular.

While the foreign ministers of the Philippines and Malaysia stressed the need for friendly bilateral relations with Hanoi, Thailand and Singapore expressed concern about Vietnam's efforts to split the association. Indonesia's Foreign Minister Adam Malik made no comment.

Singapore's Sinnathamby Rajaratnam said the Vietnese are attempted to divide and rule the ASEAN countries by making distinctions in their relations with the member governments.

"Let's not fool ourselves," Rajaratnam said, adding "We must not allow ourselves to be divided."

Thailand's Upadit Pachariyankun said that while his government supported the other ASEAN members' view that relations with Vietnam must be improved, "approaches may difer" on how to achieve this.

Thai Prime Minister Thanin Kraivichien warned yesterday that Vietnam poses "a serious threat to Thailand's security" and that "the other side" is attempting to split ASEAN through a policy of "selective preferences" in its relations with the five.

Asked if Thailand was disappointed by ASEAN's refusal to heed Thanin's appeal for greater support in the face of what he termed "general hostility" by Vietnam. Upadit said, "I don't know if they want to take a tougher line. The Malaysian foreign minister's tone was very conciliatory . . . and very constructive."

Some ASEAN leaders suggested that the associations anticipates more positive results when its leaders meet with the prime ministers of Japan, Australia and New Zealand this weekend than they achieved among themselves.

"It is psychologically easier to deal with ASEAN's external partners than to sort out the intraregional arrangements between the partners themselves," Lee said.

Prime Minister Takeo Fukuda of Japan, Malcolm Fraser of Australia and Robert Muldoon of New Zealand are to arrive in the Malaysian capital Saturday and hold discussions with the ASEAN leaders through Monday. The ASEAN government s are seeking preferential trade agreements and financing from the three visitors.