ARANYAPRATHET, Thailand (AP) _ Vietnamese forces broke a two-week lull on the battlefields of Cambodia with an assault on two resRed Cross official said some civilians were injured.

After the Vietnamese attack, 45,000 to 50,000 refugees at both camps - known as ''Site One'' and ''Site A'' - were moved about two miles deeper inside Thailand to ''Site Two,'' a senior aid official said.

''It seems both Dongruk and Sanro Changan have been occupied,'' by the Vietnamese, the aid said. Dongruk, 40 miles north of Aranyaprathet, and Sanro Changan, six miles farther north, were controlled by the Khmer People's National Liberation Front.

The sources spoke on the condition they not be identified.

The Thai military barred all reporters from the Dongruk-Sanro Changan area.

In another Vietnamese assault Tuesday, troops entered Thailand in the first ground assault on the Tatum camp, the headquarters of forces loyal to former Cambodian ruler Sihanouk, a Thai military source said.

He said the Vietnamese troops ''confronted'' Thai forces in the attack a few miles west of Tatum, about 115 miles north of Aranyaprathet. He declined to elaborate.

Tatum's more than 30,000 civilian residents were evacuated into Thailand last year as a precautionary measure.

The Sihanoukists, the National Liberation Front and the Communist Khmer Rouge joined forces to battle the Vietnamese troops that invaded Cambodia in late 1978.

The Vietnamese had not launched any major attacks on the three Cambodian resistance groups since they routed Khmer Rouge from strongholds south of the key border city of Aranyaprathet on Feb. 16.

Thai military officers said the Vietnamese and the guerrillas exchanged continuous rifle, rocket and mortar fire beginning Monday night around the two resistance camps.

This dry season, the Vietnamese have toppled virtually all Liberation Front and Khmer Rouge strongholds near the Thai border but have spared the Sihanoukists.

A spokesman for Sihanouk's office in Bangkok said the Vietnamese fired artillery into Tatum's defense lines before dawn Tuesday.

Truong Mealy said the guerrillas inflicted ''quite heavy'' casualties on Vietnamese forces making their first-ever ground assault on the mountainous, densely forested headquarters. The guerrillas suffered few injuries, he said.

He said artillery rounds struck within 1,640 feet of the Tatum camp and that the closest Vietnamese troops came was 5 miles away.

Tatum is perched on a steep precipice overlooking a wide stretch of rugged terrain that the guerrillas have ringed with land mines, barbed wire and rebel outposts.

Mealy claimed the Sihanoukists fielded some 10,000 guerrillas but would not say how many were defending Tatum. The size of the Vietnamese offensive force was not known, he said.

Earlier Tuesday, the Liberation Front claimed its men killed more than 2,000 Vietnamese troops in Cambodia in fighting in the past two months.