Vietnam has pulled back some of its troops from Cambodia's western border with Thailand in what some analysts believe could be a shift of strategy in Hanoi's current offensive against Cambodian resistance groups.

According to Thai military intelligence sources, the Vietnamese have withdrawn two or three regiments this week from the immediate area of the Ban Sangae and Nong Samet Cambodian refugee settlements, where as many as 10,000 civilians live under the control of the anticommunist Khmer People's National Liberation Front led by Son Sann. He and Thai officials repeatedly have expressed fears of a major Vietnamese attack on the camps, which could send thousands of refugees streaming across the Thai border.

Thai and western analysts still do not rule out such an attack, but they note that the pullback may signal a redeployment for a renewed attack on communist Khmer Rouge guerrillas, allied with Son Sann's group. Or it may mean the adoption of a diplomatic strategy that effectively would wind down this year's dry-season offensive, the sources say.

"It's still too early to be able to relax and say the dry season offensive is over," said one senior western diplomat. "But it may be."

According to Thai military analysts, the Vietnamese still have at least until the middle of next month to launch a major new assault on the Cambodian resistance camps before the monsoon rains begin to make movement difficult and shift the advantage to the guerrillas.

"They still have time to mount an offensive," said one Thai analyst. "They can attack Ban Sangae or Nong Samet at any time."

While western diplomats confirm that the Vietnamese pressure on those two settlements north of the Thai border town of Aranyaprathet has eased somewhat, they also are reluctant to take much comfort from the pullback, pointing out that some Vietnamese units remain in the area.

"We don't know what the Vietnamese need to have there to do something," one diplomat said.

One indication that the current lull may represent a shift from military action to diplomacy for the time being was that it began shortly after an Indochinese foreign ministers' conference in Phnom Penh last week announced that Vietnam would make another "partial withdrawal" of its forces from Cambodia next month.

Hanoi last year said that some of its Cambodia-based troops, estimated by military analysts here to total between 160,000 and 180,000, were withdrawn in August. But Thai and U.S. officials dismissed the pullout as merely a rotation of troops. Nevertheless, Vietnam declared in February it would make further "partial withdrawals" annually if conditions allowed.

However, Hanoi has consistently refused to disclose the number of troops allegedly being withdrawn, a point that makes even some of its Eastern Bloc allies skeptical.

A joint communique issued April 13 after the meeting of the foreign ministers of Vietnam, Laos and the Hanoi-installed Cambodian government in Phnom Penh also reiterated Vietnam's call last year for a demilitarized zone along the Thai-Cambodian border. Thailand rejected the idea, insisting that the Vietnamese should unilaterally pull back 18 miles from the border.

While some western diplomats say Hanoi may have been surprised by the strength of international support for Thailand during this year's Vietnamese offensive, they doubt that Bangkok's demand or any other external pressures influenced the Vietnamese decision to pull back some of its estimated 45,000 troops along the border this week.

Specifically, the analysts have shied away from connecting the Vietnamese move to fighting with Chinese forces along the Sino-Vietnamese border, or to a recent U.S. show of support for Thailand by accelerating deliveries of new, long-range artillery pieces.

Vietnam has significantly improved its defenses along its border with China since Chinese troops launched an incursion in 1979 aimed at teaching Hanoi a "lesson" for its December 1978 invasion of Cambodia. Since then, Vietnamese authorities have responded to Peking's threats of a "second lesson" by saying that they are very bad pupils.

According to Thai military intelligence sources, the Vietnamese have withdrawn at least two infantry regiments of the 5th Division from forward positions along the western Cambodian border to bases about 10 miles east along Route 69.