Noncommunist screws are tightened on Vietnam

The encirclement of Vietnam is being tightened.

But, despite the surrounding fence set up by China, the United States, and non-communist neighbors, there is no sign that Vietnam will substantially alter its policies.

The most recent tightening of screws around Vietnam is the formation of a Kampuchean government-in-exile to coordinate anti-Vietnam guerrilla actions in Kampuchea (Cambodia).

Vietnam's initial apparent response is its offer to unilaterally withdraw an undisclosed number of the nearly 200,000 Vietnamese troops that have occupied Kampuchea since the invasion of 1979.

In the past this has been raised as a hypothetical possibility. But now it has been advanced as a definite policy on the eve of a Southeast Asia goodwill tour by Vietnam's Foreign Minister, Nguyen Co Thach.

The offer is part of Vietnam's effort to punch a hole in the umbrella of unity offered by the non-communist ASEAN states - Thailand, the Philippines, Malaysia, Singapore, and Indonesia.

The offer of a troop thinning out is Vietnam's ''carrot.'' The ''stick'' is the threat that it would militarily attack a country like Thailand, if it too openly helps China to supply anti-Vietnam guerrillas in Kampuchea.

So far, most ASEAN countries have called Vietnam's carrot inadequate, although comparatively soft-line Indonesia has labelled it ''interesting.'' Most ASEAN countries have noted Vietnam has not disclosed the number of troops to be withdrawn, and that Vietnam has refused calls for international verification.

''This is an internal affair,'' a Vietnamese diplomat in Kuala Lumpur, Malaysia, is quoted as saying.

Vietnam has developed this ''internal policy'' at what is externally a most interesting time.

Earlier this month, for the first time since the Vietnamese invasion of Kampuchea, the country's former head of state, Prince Norodom Sihanouk, touched foot on Kampuchean soil. In two highly symbolic missions, he visited the guerrilla bases of the Khmer Peoples' National Liberation Front (KPNLF) and of his former enemy, the Khmer Rouge.

The visits signified the beginning of a shaky anti-Vietnamese united front.

This government preserves the separateness of its three armed parts. Given the bad feelings between the forces that make it up, there can be little certainty that it will survive.

Still the aim is to make the Vietnamese occupation increasingly costly so that some negotiation will have to take place, opening the way for restoration of Kampuchean independence.

To this end the charismatic Sihanouk, who claims 5,000 guerrillas in Kampuchea, becomes head of state. Son Sann, once Sihanouk's prime minister, again takes the job.

Son Sann claims 9,000 guerrillas in Kampuchea as part of the KPNLF. The Khmer Rouge, which ruled Kampuchea amid many atrocities from 1975 to 1979, has some 35 ,000 fighters in western Kampuchea.

So for now, at least, the screws are tigtening on Hanoi. Sihanouk and Son Sann are more likely to get Chinese supplies, after joining forces with the Khmer Rouge.

Faced with an opposition more respectable than the Khmer Rouge alone, Vietnam may have new problems getting recognition of the Heng Samrin government at the UN.

All this, in turn, may mean even more of a drain on Vietnam's already overburdened economy, if Kampuchean guerrilla forces are to be restrained.