Vietnamese troops backed by mortars and artillery continued today to probe sectors of the Thai-Cambodian border where an estimated half million refugees are massed. Khmer Rouge and anti-communist Khmer Serei guerrillas, their spirits buoyed by confirmed kills of Vietnamese troops on Wednesday, have joined forces to meet the attacks.

Military analysts withheld judgment on whether the Vietnamese advances, directed mostly against strongholds of the communist Khmer Rouge, were the start of a long-predicted dry season offensive. So far, the Vietnamese have committed only a fraction of the men they have in western Cambodia.

[Asked this week in Washington about its earlier predictions that the Vietnamese were on the verge of attacking the refugee camps, the State Department asserted that the offensive was under way.]

At a base camp outside the huge refugee shantytown known as Camp 007, Khmer Serei soldiers displayed trophies from Wednesday's fighting -- olive drab pith helmets, one of them stained with blood, and a red insignia star made of metal. "Vietnamese, Vietnamese," they shouted.

Later, while shells were heard falling in the distance, the soldiers led journalists a mile into the jungle to view three light-complexioned bodies that were said to be Vietnamese. Rightist soldiers took photos of one another standing with weapons at the ready and feet on the corpses.

Wednesday's events raised fears among reflief workers that the Vietnamese were planning to shell and disperse Camp 007 and other Khmer Serei-operated refugee settlements in the area. It was the closest a Vietnamese force had struck to these camps, which contain several hundred thousand people.

However, the attack now appears to have been aimed primarily against an important Khmer Rouge camp at Phnom Chat, about two hours' walk northeast of 007. Thai military sources say 5,000 Khmer Rouge soldiers are based there. With superior weaponry and discipline, the Khmer Rouge present a significant threat to the Vietnamese and their client government headed by Heng Samnin. Most military analysts feel the rag-tag Khmer Serei do not.

On Wednesday, the Vietnamese reportedly laid down an artillery barrage on Phnom Chat, then moved troops into the area. However, the advancing force encountered a joint defense force of Khmer Rouge and 007's Khmer Serei, who had put aside political differences to expel the foreign army.

It is an irony of the Cambodian conflict that these two groups should be drawn into alliance. Many Khmer Serei troops served in the U.S.-supported Lon Nol army, which the Khmer Rouge defeated and broke up in 1975. However, hatred of the Vietnamese has overcome the hatred the two Cambodian factions have for each other.

Khmer Serei commanders said the Vietnamese penetrated to the second line of defense, then withdrew after suffering seven dead. Cambodian casualties were described as one killed and an unknown number wounded.

Later Khmer Rouge guerrillas, easily recognized by their green uniforms, soft hats and rubber-tire sandals, could be seen picking up food and other supplies at 007, which functions as a marketing center for refugees in the area. Khmer Serei troops listened politely as a Khmer Rouge officer briefed journalists on the fighting.

Shelling continued in the Phnom Chat area yesterday and today. Casualties continued to arrive at clinics operated by foreign doctors but details were not available on the outcome of the fighting.

A small number of civilians fled Phnom Chat during the attack but it had little visible effect on the morale of civilians in 007.

In two Khmer Rouge settlements south of the Thai town of Aranyaprathet, there were few signs that the past week's intensified fighting there had changed the pace of life. "We're still here," said a French-speaking cadre with nonchalance. "We're waiting for the Vietnamese to come."

Internationally donated food and medicine that began flowing into border villages like these late last summer have worked wonders for the people's health and spirits. One no longer sees babies close to death from malnutrition or families immobilized by malaria.

Today, Khmer Rouge women walked into Thai territory to pick up bags of rice provided by relief agencies. Balancing sacks on their heads, they returned in single file toward a crude wooden bridge spanning the stream that marks the border.

In thatch huts, women stitched together the black pants and shirts that are the standard garb in Khmer Rouge society. Others ground rice into paste to make noodles. People tended small gardens and worked at making charcoal, which is sold to Thai farmers.

There were signs of war, however, such as small bunkers outside many huts. Here and there, young men could be seen with AK47 rifles slung barrel-down over their shoulders.

Women outnumbered men, many of whom apparently were doing military duty elsewhere.

"Go a kilometer and a half that way," said a young woman gesturing into Cambodia, "and you'll run into Vietnamese."

In one settlement's field hospital, a series of plastic shelters set up in a grove, about 25 men and women were recovering from bullet and shrapnel wounds. Several had lost feet by stepping on mines. They waited patiently for Cambodian medics to dress their wounds.