The Vietnamese-backed Cambodian rebels, tightening their grip on the country, announced today that they have captured all major cities and the famed Angkor Wat temple complex, symbol of Cambodian nationalism.

An announcement by the new government in Phnom Penh said its troops yesterday entered Cambodia's second largest city, Battambang, the center of the country's rice growing region, and Siem Reap in the northwest near the scene of fierce fighting for several days.

The new rebel victories coincide with a call for an immediate and complete withdrawal of foreign troops from Cambodia issued by the foreign ministers of five Southeast Asian countries today.

Ministers from countries represented in the Association of Southeast Asian Nations (ASEAN) declared that Cambodians should determine their own future "free from interference or influence from outside powers."

Their resolution, adopted after a two-day emergency meeting here, was primarily directed at the U.N. Security Council debate on Cambodia and did not imply that the five countries might take joint action against Vietnam for sending troops, tanks, and planes to help insurgents who have almost occupied the country.

There was no independent confirmation of Phnom Penh's new victory claims.

If the claims are true, the new Cambodian government is now in substantial control of almost all population centers, although Western diplomatic sources pockets throughout the country.

The fighting was getting closer to Thailand's borders as the troops of the old government retreated in the face of powerful Vietnam-led tank and aircraft assaults.

In the border town of Aranyaprathet this morning, reporters coud hear artillery or tank fire about 15 miles across the frontier in Cambodia. During the previous night, Thai farmers and soldiers said tey could hear small arms firing from the Cambodian side for nearly six hours and that it seemed to be much nearer than on previous nights.

The statement by ASEAN foreign ministers reflected the alarm felt by all five anticCommunist nations in the region at Vietnam's intervention. ASEAN is essentially an economic organization that does not usually act in political or military spheres. Its members are Thailand, Malaysia, Indonesia, the Philippines and Singapore.

All five are concerned about the effects of Vietnam's actions on Communist guerilla movements in their own countries.

It also underscored the collapse of the five nations' burgeoning relations with Vietnam, which had gotten off to a warm beginning only a few months ago.

Last fall, Vietnamese Premier Phan Van Dong made a goodwill mission through the ASEAN region, assuring each government that his administration seeks their friendship. As a gesture of proof, he assured each that Vietnam would not seek to interfere in the internal affairs of other Asian countries.

Now, ASEAN'S ministers are skeptical of Vietnam's promises and the resolution adopted here today was intended as a rebuke to the Vietnamese premier, the foreign ministers said.

After what has happened in Cambodia, the premier's pledge has been "undone," declared S. Rajanatnam, Singapore's foreign minister who acted as spokesman for the five ministers.

"This statement is a request to Pham Van Dong, an appeal to Pham Van Dong, to restore his credibility Rajanatnam said at a news conference.

"We want to be friends with Vietnam, but we want Vietnam to reassure us," he continued. A withdrawal of that country's forces from Cambodia would go far toward restoring Vietnam's credibility, he said.

But he also made it clear that Asean is not contemplating any action to compel a Vietnamese withdrawal. Asked what Asean would do if Vietnam refuses the request, Rajanatam noted the current debate in the U.N. Security Council and said, "It is a question of what the United Nations will do."

Vietnam has attempted to justify its intervention partly by claiming Pol Pot's troops had made border raids against Vietnamese villages and partly by insisting that it acted to stop the alleged genocide of the Cambodian people.

In a new defense of its actions today, Vietnam said Pol "Pot's forces had "launched a border war" against Vietnam as early as 1975.

In an official radio broadcast, Hanoi