Vietnamese troops occupying Cambodia are purging suspected resistance sympathizers among provincial officials of the Hanoi-installed government, causing thousands of villagers to flee to camps on the Thai border, according to refugees and resistance leaders.

The reported crackdown is seen as part of a Vietnamese effort to consolidate control over the countryside in Cambodia, which Hanoi's troops invaded 4 1/2 years ago. Another aspect of this effort--and a reason some refugees cite for fleeing their homes--is increased Vietnamese settlement in Cambodia .

The foreign ministers of the noncommunist Association of Southeast Asian Nations (ASEAN) expressed their "serious concern" Saturday at these "reported demographic changes being imposed by the Vietnamese occupation forces" in a number of Cambodian provinces.

The situation in Cambodia was discussed for two hours in Bangkok Monday morning by visiting Secretary of State George Shultz and the ASEAN foreign ministers representing Thailand, Indonesia, Malaysia, the Philippines and Singapore, Washington Post correspondent Don Oberdorfer reported.

A U.S. spokesman said Shultz compared the situation to that in Central America, where he said "a vast flow of Soviet arms is going to Cuba and Nicaragua" with the aim of destabilizing the countries of the area.

According to officials of the main noncommunist group opposing the Vietnamese occupation, more than 4,000 Cambodians have reached this camp opposite the Thai village of Ban Sangae since Hanoi's troops began their crackdown in the Siem Reap area on May 25.

Thach Reng, a former Cambodian general and now a commander of the Khmer People's National Liberation Front which controls this camp, said the Vietnamese have arrested 300 provincial cadres of the government they installed in Phnom Penh in 1979.

Thach Reng said the government employes, who included teachers and local administrators, were accused of having links with the front. He said the accusations often were "more or less true," but that not all of the arrested cadres were agents for the front.

He said those arrested were replaced by military cadres from the Heng Samrin army's 3rd Division. Thach Reng claimed that some have been executed. One refugee, Pin Vuon, 38, said he led 450 residents of his Svey Snom district to this camp after the Vietnamese killed the district chief and a member of the administrative committee.

The reports, if true, would indicate a toughening of the Vietnamese occupation of Cambodia. During its first three years, there had been relatively few reports of abuses against civilians by Vietnamese troops.

The reported crackdown might also indicate a new tack in the Vietnamese war against the Cambodian resistance groups based along the border with Thailand.

Since the Vietnamese halted their dry-season offensive in April after overrunning several resistance camps, there has been little fighting along the border. With the onset of the monsoon rains last month, the guerrillas have taken the initiative with hit-and-run attacks on Vietnamese positions inside Cambodia, according to resistance leaders. Thus the crackdown could be aimed at denying the noncommunist guerrillas support in the interior, they said.

According to Hing Kunthon, a member of the executive committee of the Khmer front, many residents of western Cambodian districts under Vietnamese control have relatives among the 200,000 Cambodians living in camps controlled by the resistance groups.

"Up to now they have been supporting our activities," he said of these interior residents.

He said that in addition to purging Cambodian cadres, Vietnam was pushing ahead with plans to settle Vietnamese civilians in Cambodia, especially the western part.

"We think in the future it might be a big problem," he said.

In a news conference in Bangkok Saturday, Thai Foreign Minister Siddhi Savetsila said that according to Thai intelligence reports, Vietnam has a five-year plan to settle 300,000 Vietnamese civilians in Cambodia. He said that in 1982 alone 150,000 settlers from Vietnam, which has a population of 55 million, had established themselves in Cambodia, with less than 7 million inhabitants.

Siddhi said the principal settlement sites were along the Mekong River and around the Tonle Sap lake, where the Vietnamese are engaged in fishing and commerce.

Hanoi has sought to portray the settlement policy as a short-term measure to help the Cambodian economy. But Cambodian resistance leaders and Thai officials view it as part of a plan to change the face of Cambodia and consolidate Vietnam's grip.

"It means the Vietnamization of Cambodia," said Squadron Leader Prasong Soonsiki, the head of Thailand's National Security Council.