Behind military and political moves in Southeast Asia

The recent round of fighting on the Chinese-Vietnamese border seems to have had a political rather than a military objective. In shelling Vietnamese border provinces and, if Hanoi is to be believed, sending infantry into Vietnam, the Chinese were apparently signaling their support for Thailand and their displeasure with Vietnam over the recent fighting along the Thai-Kampuchean frontier.

The Thais undoubtedly appreciated the gesture, but it is unlikely to deflect Vietnam's attention or its troops from Kampuchea.

Military observers say that Vietnam's border with China is far better defended now than it was in February 1979, when China launched a full-fledged invasion.

At that time, Hanoi reportedly had seven regular divisions, supported by an unspecified number of regional forces, defending the border. It could also call on another five regular divisions in general headquarters reserve.

Today Vietnam is believed to have 12 divisions on the border, supported by a further seven divisions between 25 and 40 kilometers (16 and 25 miles) from the border.

It can also count on about four divisions in general headquarters reserve, presumably in Hanoi.

These figures, if correct, suggest that only a very large Chinese attack on Vietnam's northern provinces would cause Hanoi even to consider pulling any troops out of Kampuchea.

As usual, it is virtually impossible to determine exactly what happened on the Sino-Vietnamese border last week. Most belligerents differ in their description of an incident. The Vietnamese and the Chinese rarely agree an incident took place.

The Vietnamese say that on April 6 ''a number of battalions'' of Chinese infantry crossed into the Vietnamese province of Lang Son. They occupied two hills until the morning of April 7, when they were reportedly pushed back.

The Chinese say the Vietnamese story is fiction. No Chinese incursion took place, they claim.

The Chinese do, however, admit shelling the Vietnamese border in a number of places since the beginning of the month. Publicly they say this was in retaliation for similar Vietnamese actions. Privately they agree that the real cause of their shelling might have been the Vietnamese incursion into Thailand late last month.

For once the Vietnamese agree. In fact, they are trying to make political capital out of the border shelling.

The Chinese attacks, Hanoi says, were designed to take the pressure off the Khmer Rouge who in the recent Vietnamese attacks had ''lost even the ammunition stores that the Peking reactionaries and Bangkok had built for them.''

This and other verbal barrages in similar vein suggest that the Vietnamese have abandoned any pretense at conciliation toward the Thais.

The harshest verbal assault came from the Vietnamese Foreign Minister Nguyen Co Thach.

During his stopover in Bangkok at the end of last month, Mr. Thach canceled a meeting with his Thai counterpart, Siddhi Savetsila. Thach was almost certainly alerted by Hanoi of an impending Vietnamese attack against a Khmer Rouge camp on the Thai border.

About a week ago, however, Thach told the official Vietnamese news agency that Bangkok had no interest in an agreement over Kampuchea.

''The truth is,'' Thach said, that both China and Thailand ''do not want to be bound by peace agreements. They want to be free to cause tension'' along the Sino-Vietnamese and Thai-Kampuchean borders, ''to support the Pol Pot reactionaries.'' Vietnamese troops toppled Pol Pot's Democratic Kampuchea government in January 1979.

Last weekend, Radio Hanoi repeated claims that the Thais and Chinese were working together in a ''preplanned and coordinated manner.'' The Vietnamese also accused the Thais of allowing Vietnamese exiles opposed to the Hanoi government to set up a radio station on Thai territory.

The aim of their verbal attacks - portraying the Thais, Chinese, and Khmer Rouge as working in close alliance - seems once again to be to drive a wedge between Thailand and its allies.

Several of Thailand's colleagues in the Association of Southeast Asian Nations (ASEAN), particular Indonesia, are unhappy at the idea of being too close to the Khmer Rouge.

They also have considerable reservations about getting too close to the Chinese. Vietnam, it seems, hopes to exploit these fears.

Although officially denying that their troops crossed into Thai territory late last month, the Vietnamese have admitted the incursion in private diplomatic briefings to their allies.

Their main target, they claim, was a large Khmer Rouge troop concentration and an ammunition supply dump. The Vietnamese say the dump was partly or totally in Thai territory. The Thais say the dump was in Kampuchea. (Much of the Thai-Kampuchean border is defined more by local tradition than international law.)

During the 10 days that followed the Vietnamese incursion on March 24, Thai airstrikes destroyed the dump, killing a number of Vietnamese troops who had captured it. Journalists who later visited the area of the fighting in the Thai province of Sisaket report that Khmer Rouge troops seem to have retreated into Thailand.

There are indications that the Vietnamese are planning more attacks on anti-Vietnamese bases along the border. Several days ago, the Khmer Rouge reported losing one of its forward positions defending the important Khmer Rouge base of Phnom Malai. The Khmer Rouge said Friday it recaptured the base.

(Reuters reported Sunday that tank-supported Vietnamese troops attacked the Khmer Peoples National Liberation Front headquarters at Ampil near the Thai-Cambodian border Sunday, causing thousands of refugees to flee into Thailand's Aranyaprathet Province, according to a senior Thai official.

Ampil was not only the headquarters of the KPNLF but also believed to have contained more than half of the KPNLF's military strength of approximately 5,000 to 6,000 fighters. If the reports are indeed correct, Ampil represents a major loss to the coalition.

Other troop movements are reported in the southern part of the Thai-Kampuchean border. Sources close to the Vietnamese, say that Hanoi plans more military assaults before the monsoon rains set in at the end of April.