A Thai helicopter today rescued former deputy premier of Cambodia Ieng Sary as the Vietnam-backed rebels who overthrew his government pushed toward the Thai border to complete their swift conquest of the country.

Ieng Sary was flown to Bangkok and then quickly to Hong Kong en route to China after being refused permission to enter Thailand and remain long enough to argue the case for his fallen regime.

Thailand's Prime Minister Kriangsak Chamanand told reporters that Ieng Sary had sought a meeting with him to explain Cambodian developments. The request was refused because "we alrealy know the situation" in Cambodia, he said.

[Ieng Sary arrived in Hong Kong with a party of ten and left early Friday morning by car for Canton, Post correspondent Jay Mathews reported. Mathews reported that Sary was scheduled to catch a flight in Canton for Peking.]

About 1,000 survivors of the fallen Pol Pot government were reported near a Thai border crossing, waiting final permission for a quick exit through to safety. Khieu Samphan, the former president, is believed to be among those waiting to flee Cambodia.

Thai sources indicated that the government will permit them to cross the border and pass through Thai territory to reach a former U.S. air base at Utapao, where they may board a Chinese ship.

But the Thai prime minister, trying to dampen fears that Thailand would be swamped by a new wave of Cambodian refugees, said no refugees would be permitted into the country.

Thailand is also determined, as part of its neutrality, to refuse entrance to remnants of the battered Khmer Rouge army. It is expected that some of them will attempt to enter. Thailand anyway in their flight from the conquerors and some observers expect border clashes as Thais try to keep them out.

Thailand has agreed to grant quick transit to those former high government officials who might suffer most if captured by the rebels.

Kriangsak told reporters that the Chinese ship is due to arrive in "a few days" at the former U.S. base located about 100 miles southeast of Bangkok. It was dispatche to pick up several hundred Chinese advisers and other foreigners who escaped two days ago.

There were unconfirmed reports of clashes near the Thai border as the Vietnam-backed insurgents sought to mop up the fleeing army.

Kriangsak told reporters that a Vietnam-led force was pushing through Pursat Province, which borders on Thailand.

Although worried about the possibility of fighting reging on or near their border, Thai officials have not put into effect any large-scale defense preparations. Border security has been strengthened somewhat, but no full scale alert has been ordered.

Kriangsak apparently feels that his first priority is to prevent any outbreak of fears in his country. His first act when the rebels took Cambodia's capital of Phnom Penh early this week was to urge citizens not to "panic."

He asserted that neither Vietnamese nor Cambodian troops would enter Thai territory.

"Thailand," he added, "is a friend of everybody." He has met throughout the week with military advisers to develop a defense contingency plan.

To reassure the Thais, Vietnam's ambassador yesterday reaffirmed the two countries' pledges not to interfere in each other's internal affairs. That commitment was made in a joint communique last fall when Vietnam's Premier Pham Van Dong visited Thailand. It was before the Vietnamese stepped up their ared activities in eastern Cambodia which ultimately turned into the total rout.

The Vietnamese ambassador, Hoang Bao Son, insisted that Cambodia was a "particular case" and would not be a model for insurrections in other Southeast Asian countries.

He said Vietnam had supported the Cambodian rebels because of alleged border intrusions against Vietnam by the regime of Pol Pot.