Cracks are appearing in the united front the Western-oriented countries of Southeast Asia have erected against Hanoi and the government it installed in Cambodia 17 months ago, many analysts here believe.

Malaysia and Indonesia apparently feel that their policy of confrontation -- applauded by Peking and Washington -- could lead to excessive Chinese influence in the region.

Vietnamese Foreign Minister Nguyen Co Thach has launched a diplomatic offensive evidently designed to exploit this breach in the ranks.

In talks in Malaysia last month, he reportedly hinted at cosmetic concessions aimed at winning diplomatic recognition for the Cambodian government from its noncommunist neighbors and the rest of the world.

Some diplomatic observers believe Thach suggested that Malaysia and Indonesia send observers to elections scheduled in Cambodia for late this year. To date, however, nothing has been confirmed officially.

Malaysia and Indonesia are members of the Association of Southeast Asian Nations (ASEAN), the economic and political grouping that also includes Thailand, Singapore, and the Philippines.

Shortly after Hanoi's troops drove across Cambodia and overturned the Khmer Rouge government early last year, ASEAN issued a strongly worded statement calling for complete withdrawal of Hanoi's forces and U.N.-supervised elections.

U.S. officials welcomed the statement, the toughest example of political solidarity in ASEAN's 13-year history. Observers pointed out that only Thailand shared a border with Cambodia and was directly threatened by Vietnamese forces.

During 1979, Thailand drifted into closer cooperation with China, which continued to supply the remnants of the Khmer Rouge Army. Peking, meanwhile, pledged to come to the aid of Thailand if it were attacked by Vietnam, though no formal treaty or military aid program was established.

However, there have been signs that over the past year Malaysian and Indonesian leaders have begun wondering if ASEAN is not allowing China to drag it into a Chinese dispute with Vietnam.

Both ASEAN countries have histories of racial tension involving powerful Chinese minorities. In 1965 Indonesia's pro-chinese Communist Party came close to taking control of the government. Diplomatic ties with Peking were suspended and still have not been normalized.

Anti-Chinese sentiment is still so strong in the Indonesian government that censors have been known to black out photographs in foreign publications that happen to show Chinese characters.

Although Vietnam flooded Indonesia and Malaysia last year with thousands of unwelcome boat people, suspicion of the Chinese appears to remain more deeply rooted.

In March, Indonesia and Malaysia came up with the "Kuantan Formula" for solving the Cambodian impasse, following a summit meeting of their leaders in the Malaysian town of Kuantan.

According to the formula the key to peace and stability in Southeast Asia is to remove Vietnam from the influence of both the Soviet Union and China. i

Analyst also noted that is suggested that Vietnam's ideal role could be as a bulwark against Chinese influence in the Southeast Asian region. This was a clear allusion to the danger from Peking, the analysts said.

Early in May, Vietnamese Foreign Minister Thach flew to Malaysia for talks. Afterwards, Malaysian Prime Minister Hussein Onn said Vietnam had revealed significant changes in its position, raising new hopes for a political settlement in Cambodia. He declined to say what the changes were, however.

At a press conference in Bangkok, Thach denied knowledged of such changes, but some diplomatic sources say he in fact suggested that Malaysia, Indonesia and Vietnam's ally, Laos, send observers to the forthcoming Cambodian elections.

Thach was said to have proposed that other representatives of these three countries be stationed on the Thai-Cambodian border to prevent fighting from spilling into Thailand. Thailand last fall asked the United Nations to post observation teams there.

One ASEAN diplomat scoffed at the idea of a role in Phnom Penh's elections.

"Our credibility would be that of an infant if we were to participate in this fraudulent exercise," he said.

Indeed, it appeared extremely unlikely that ASEAN as a whole would accept such a proposal, or that Malaysia and Indonesia at this point feel strongly enough about a Chinese threat to proceed on their own.

By doing so they would risk close economic and political ties with Thailand, which maintains a hard line toward Phnom Pehn. Thai officials privately aruge that three to five years of continued military pressure by Khmer resistance groups is the only way to bring an acceptable solution in Cambodia.

Vietnam could offer little to Malaysia and Indonesia in return, except, perhaps, a confidential promise not to unleash another tide of boat refugees.

Still, events of the past months suggest strongly that there is at least a small breach in ASEAN's ranks. Vietnam can be expected to do everything possible to widen it, while consolidating its control over Cambodia.