Vietnam is using rapid-fire tactics against Khmer guerrillas in Kampuchea. On Saturday, Vietnamese troops captured and occupied the remote Khmer People's National Liberation Front (KPNLF) base of Baksei, located in the so-called tri-border area, where Kampuchea (Cambodia), Thailand, and Laos meet. The KPNLF is the larger of the two noncommunist groups opposed to the Vietnamese presence in Kampuchea.
The civilian population of Baksei, some 1,500 people, is reported to have fled into Thailand. KPNLF sources say four of their guerrillas were killed.
On Tuesday, the Vietnamese struck at a camp on the Thai-Khmer border in the far south. The headquarters of the KPNLF southern command at Sok Sann was hit by an artillery barrage at dawn, followed by a ground assault.
Even in some areas occupied by the KPLNF, the Vietnamese effectively call the shots.
On Sunday a group of reporters tried to visit the Khmer guerrilla camp of Nong Chan. A Thai Army soldier stopped us a kilometer from the camp. There had been shelling in Nong Chan that morning. A guard at the last Thai checkpoint said it was dangerous to go any further.
He was proven right a few minutes later, when about 20 rounds of 130 -millimeter artillery hit Nong Chan. Smoke rose from the camp center, which is now deserted except for guerrillas of the KPNLF. There was no answering fire.
From their sandbagged positions on top of the ditch, Thai troops counted the shells. Three Khmer guerrillas who had been standing by the checkpoint strapped on their ammunition belts and wandered off toward the camp. Two others posed for pictures by the tank ditch.
Throughout the shelling a couple of Khmer children kept on fishing in the water-filled moat on the Kampuchean side of the ditch, while on the other side Thai peasants continued with their harvesting.
Press reports in Bangkok the morning of the shelling had announced the KPNLF had reoccupied camp. After two weeks of fighting, the Vietnamese had pulled out.
This suggested that normalcy would soon return to Nong Chan. The impression of normalcy was rather misleading. The shelling showed that the Vietnamese did not need to occupy the camp to control it. For the time being at least, they have turned it into a no man's land. They can keep it that way almost at will.
The former civilian inhabitants of the camp, about 23,000 of them, are spread along the border in large shantytowns of makeshift tents roofed with UN blue plastic sheeting. The majority of them are in Site 6, one of the evacuation areas prepared by the United Nations in anticipation of attacks on the border settlements.
There seemed to be babies everywhere, many of them just a few months old. Outside some tents a few vegetables were spread out for sale. A peddler with a game of chance had collected a large crowd. And, under an awning placed against one of the few surviving trees, the inevitable barber had set up shop.
It will be some time before they go back to the main camp. The fighting has leveled much of it, and there are mines everywhere. As KPNLF guerrillas retreated, they laid mines. When the Vietnamese moved out, they did the same. These, a civilian official at the camp says, caused most of the KPNLF casualties.
''During the fighting we lost 20 dead and over a hundred wounded,'' a senior camp official said. ''Most of the casualties were caused by our own mines,'' he added.
As he talked he was handed a list of 11 more guerrillas who had just died of their wounds. Vietnamese losses, the official claimed, were much greater: at least several hundred killed, including one lieutenant colonel.
The Vietnamese casualty figures came from smugglers and traders who travel regularly from Nong Chan into the interior. Nong Chan in particular is the center of the contraband business - a fact that is something of an embarrassment to the KPNLF leadership.
The Nong Chan military commander, Chea Chhut, is more akin to an old-style warlord than a modern guerrilla commander. He is, however, an effective fighter.
KPNLF officials and commanders in the camps feel that the Nong Chan attack was simply a prelude to a bigger Vietnamese attack that will probably be directed against Ampil, the KPNLF headquarters about 15 miles north of Nong Chan. They think the assault is imminent.
More military supplies have arrived for the KPNLF. At both Site 6 and Nong Samet (population 62,000 plus 2,000 to 3,000 guerrillas), many of the guerrillas seen were carrying brand new SK Combat rifles.
Officials at Site 6 said they had received 500 to 600 guns at the beginning of December. A guerrilla commander in Nong Samet said 250 weapons had arrived on Dec. 1. A packing list for the rifles indicated they were probably of Chinese manufacture. (In early October Peking promised the KPNLF weapons for 3,000 men. This is the first sign the weapons have arrived.)
The problem is that in the short term at least the weapons will be used for defending large camps, not for small-scale guerrilla operations. The KPNLF has pulled back most of the guerrillas who had previously operated between 12 and 37 miles inside Kampuchea. The Vietnamese clearly hope to keep them bottled up in the border camps, unable either to infiltrate Kampuchea or support other guerrilla bases which may be attacked.