Southeast Asia's noncommunist nations appealed to foreign powers today to step up military aid to Cambodian resistance groups battling the Vietnamese occupation of their country in view of Hanoi's current successful offensive along the Thai-Cambodian border.

In a joint communique issued after talks on the Cambodian situation, the foreign ministers of the Association of Southeast Asian Nations (ASEAN) -- which includes Thailand, Indonesia, Malaysia, Singapore, the Philippines and Brunei -- called on "the international community to increase support and assistance to the Kampuchean [Cambodian] people in their political and military struggle to liberate their homeland from foreign occupation."

Asked in a press conference if this meant ASEAN was seeking direct foreign military aid for the resistance, Thai Foreign Minister Siddhi Savetsila replied, "Yes."

He said it was an open secret that Afghan "freedom fighters" were receiving considerable help from abroad and that Cambodian resistance fighters also were "entitled to fight for their independence."

"They can't fight with their bare hands," he added. "As long as the Soviet Union keeps sending tanks, artillery and all sorts of weapons to the Vietnamese , how do you expect these Kampucheans to survive if they have nothing?"

ASEAN diplomats said afterward that the appeal represented a tougher position and a desire to increase military pressure on Vietnam in the face of the current dry-season offensive. Since the drive began in November, Vietnamese troops have overrun every major noncommunist resistance base and now are bearing down on strongholds of the more powerful communist Khmer Rouge guerrillas.

The diplomats said the appeal was directed primarily at the United States, although there was no sign that Washington was willing to change its policy of providing only humanitarian and diplomatic support to the resistance. Currently, China provides the bulk of the military aid to the resistance, principally the Khmer Rouge. Thailand and Singapore are known to aid the noncommunists militarily.

The communique marked the first time that ASEAN as a group has called for direct foreign military aid to the Cambodian resistance.

"Before, we hedged on the military aid question, but now in the face of the Vietnamese offensive we couldn't be seen to be wavering," one diplomat said. He said ASEAN "hopes that given the new military situation on the ground, the Reagan administration will focus" on the issue.

"There is a greater willingness to state publicly that there cannot be a political solution without greater military pressure on the ground" against the Vietnamese in Cambodia, an ASEAN foreign minister said. "Now we must go all out to build them [the resistance groups] up in military terms."

After the joint communique was issued, the foreign ministers conferred at an undisclosed location with leaders of the U.N.-recognized Cambodian coalition government comprising three resistance groups. An ASEAN diplomat said the foreign ministers found the three leaders -- Prince Norodom Sihanouk, Son Sann and Khieu Samphan -- in high spirits despite the major Vietnamese offensive.

Sihanouk heads the coalition government. Son Sann leads the major noncommunist group, the Khmer People's National Liberation Front, and serves as the coalition's prime minister, while Khieu Samphan, titular head of the communist Khmer Rouge, is vice president in charge of foreign affairs.

The discussions coincided with reports of heavy fighting between Vietnamese troops and Khmer Rouge guerrillas defending their Phnom Malai base area in western Cambodia south of the Thai border town of Aranyaprathet. The Vietnamese have launched a pincers attack against the Khmer Rouge strongholds, but details of the fighting have been sketchy.