More than 30,000 Cambodians, some of them heavily armed Khmer Rouge soldiers of ousted premier Pol Pot, crossed into Thailand today in flight from Vietnamese forces, Thai authorities said.

The massive crossings occurred in Chantaburi and Trat provinces in the far southeast corner of Thailand. The region is just to the northwest of Cambodia's Cardamom Mountains where Pol Pot reportedly has tried to establish a guerrilla base since the Vietnamese invasion that toppled his government earlier this year.

About six weeks ago, the Vietnamese and their Cambodian allies launched an offensive against the remaining pockets of Khmer Rouge resistance. Since then there have been several occasions when thousands of Cambodians, including some military, have fled into Thailand. Most of the civilians have been forced to return to Cambodia under pressure from both Thai and Khmer Rougr troops.

According to Thai authorities, the Cambodian soldiers participating in the current exodus are considerably better armed then those who crossed previously. The Thais say that they have collected such things as mortars, rockets and heavy machine guns from the Cambodians. This has prompted speculation that the troops were from one of Pol Pot's elite units.

It is not known how many troops Pol Pot still has under his command but generally they are thought to number about 30,000. Before the Vietnamese invasion, there were about 70,000 in Cambodia's armed forces.

Thai authorities described the situation today as "critical" and "extremely dangerous." They expressed fear that the Vietnamese might prusue the Khmer Rouge troops across the border.

The Thai policy of trying to get the refruees to return across the border has created severe strains in its relations with Hanoi. Vietnam has charged that by doing so Thailand has abandoned its policy of neutrality.

In a related development, the official Vietnam News Agency today denied an account carried in Thai newspapers that said the Vietnamese-led forces in Cambodia had threatened to attack the Thai border town of Aranyaprathet.

A broadcast report said that the news agency was "authorized to declare that this report was a fabrication with the bad intention of sowing discord between the Thai people and the people of Vietnam."

Prime Minister Kriangsak Chamanan of Thailand told reporters today that it was Thai policy to push the Cambodians back across the border but that this was difficult in the case of the sick, the elderly and children. These, he said, would be taken to camps and cared for.

Thailand adopted a tough policy in regard to the Cambodian refugees after its facilities were swamped by hundreds of thousands of refugees from that country, Laos and Vietnam over the past four years.

Recently, however, the Thai position has been complicated by the appearance of ethnic Chinese among the refugees from Cambodia. To push the Chinese back might anger Peking, something that Bangkok has been trying to avoid.

Some ethnic Chinese refugees said today that the Pol Pot government killed more than 500,000 of them before it fell in January.

One hundred and fifty Chinese living in a temporary camp at the border town Aranyaprathet, said in an open letter that Cambodia's Chinese population had fallen from 600,000 when Pol Pot seized power in 1975 to 40,000 now.

The refugees accused of Pol Pot's government with torture, including gouging out eyes and other mutilations. There was no confirmation of the charges but over the years there has been claims that the Khmer Rouge government executed hundreds of thousands of its citizens.

Western analysts, noting the periodic flight of thousands of refugees from the Cambodian fighting, speculated that this may be the result of Vietnamese tactics.

When on the attack, they said, the Vietnamese may always take care to see thet an escape corridor remains open so the Khmer Rouge troops are never trapped in a fight-or-die situation.