Reagan absence in Jakarta sends another signal to Southeast Asia

This was the weekend President Reagan was supposed to have been in Indonesia. But instead, only the usual collection of businessmen is here, eager to trade with a country of enormous potential wealth but widespread poverty.

Jakarta was to have been Mr. Reagan's first stop on his Asian tour: Now he will go only to Japan and South Korea. The official reason for not coming here was the pressure of commitments with the legislative process in Washington, but few doubt the real reason.

''We all know he canceled because of the troubles in the Philippines,'' said a member of Indonesia's assembly. ''But,'' he added, ''just because one country in the region is in trouble, it does not mean we all are.'' Indonesians feel that, not for the first time, they have been treated in a cavalier fashion by the United States.

Mr. Reagan's primary purpose here was to meet the foreign ministers of the Association of Southeast Asian Nations (ASEAN) - Indonesia, Thailand, the Philippines, Malaysia, and Singapore.

Now, discussions go on without him, and although the threat of the downfall of the Marcos regime is not on the agenda, it is undoubtedly one that worries ASEAN. Four of the five nations have been forced to contemplate just what their response would be if one of their group was faced with violent upheaval, particularly if this looked like bringing in a left-wing government. Would the philosophy of musyawarah,m the Indonesian word for dialogue leading to consensus and the term Singapore President Lee Kuan Yew used to sum up the ASEAN approach, still apply?

Or would the other members make moves toward forming a military alliance to safeguard their communal interests? Already many have talked darkly about the growth of Soviet forces in the area, based in the old US strongholds in Vietnam. Vietnam's presence in Kampuchea is seen as concrete evidence of the left's threat to Southeast Asia.

Ever since the Vietnamese tanks moved into Phnom Penh in early 1979, ASEAN has led a vigorous fight at the UN and elsewhere against Vietnam. They have successfully had the credentials of the Hanoi-backed Heng Samrin regime rejected by the UN and have recently encouraged support for a coalition of the three Khmer resistance groups.

ASEAN's main hopes for a settlement of the Kampuchea question are now, according to Indonesian Foreign Minister Mochtar Kusumaatmadja, pinned on an appeal recently made by ASEAN foreign ministers calling for a partial withdrawal of Vietnamese troops from Kampuchea on a territorial basis, beginning with a withdrawal from territory adjacent to the Thai border. A clear response from Vietnam is still awaited. Meanwhile, Mr. Mochtar says, ''We have lots of patience.''

ASEAN has shown itself to be increasingly sensitive on the Kampuchea question. So angry was it with Australia's refusal to cosponsor this year's UN resolution on Kampuchea that there was immediate talk of sanctions. Annual trade discussions between the group and Australia were canceled.

Jakarta already has its own quarrel with Australia. Indonesia's move into the former Portuguese colony of East Timor in 1975 was strongly condemned in Canberra, particularly by Robert Hawke, who was then in opposition but whose Labor Party now holds power. Though there have been signs lately that Australia's position is softening, the whole affair touches a raw nerve in Jakarta.