One of the extraordinary things about the protracted border war between Vietnam and Cambodia is that China's rhetorical support for its allies in Phnom Penh is not being matched by an significant infusion of aid.

Since the skirmishing along the Vietnam-Cambodia border escalted into large-unit battles late last year, there has been no great increase in the level of Chinese military assistance to Cambodia, analysts here said. In particular Peking has made no attempt to raise the level of Cambodia's firepower to that of the heavily equipped Vietnamese.

There are slightly more Chinese economic and military advisers in Cambodia than a year ago, with the total now put at 2,000 to 3,000. The military advisers' role, however, seems limited to training troops with no indication that they are engaged in planning or carrying out the fighting.

Analysts here differ on what is China's true attitude toward the Communist government in Phnom Penh. Some think Peking may be relatively indifferent to the fate of a country that has been widely condemned for its ruthless domestic policy. Others think China would take strong action if Hanoi moved to bring down the Cambodian government.

Analysts note that Vietnam is becoming more and more insistent in urging the Cambodian people to revolt. A Cambodian defector said at a recent news conference in Vietnam that Khmer troops should turn their guns on their officers.

On Tuesday, the Vietnamese Communist Party newspaper Nhan Dan said: "Cambodia has a fascist-administration which has genocide as a national policy. It would in fact be no surprise if there were a popular uprising against the Cambodian government."

Such comments give further credence to Phnom Penh's claim that Vietnam's true goal is to install a docile puppet government in Cambodia.

Recently there have been signs that the Vietnamese are training Cambodian youths to fight against the Phnom Penh government. An estimated 100,000 Cambodians are said to have fled into Vietnam following the social upheaval instigated by the Communists following their victory in April 1975. The refugees joined about 1 million ethnic Cambodians already living in the southern part of Vietnam.

There is a consensus that it would be foolhardy, both militarily and politically, for the Vietnamese to drive all the way to Phnom Penh. Nevertheless, analysts do not rule out the possibility that Hanoi may try to establish a regime to challenge Phnom Penh in the eastern part of Cambodia, possibly centered on the Parrot's Beak-Mimot area.

Opinions vary on the magnitude of the recent offensive launched by Vietnam. Some analysts think the number of troops involved may be as high the 60,000 reported earlier this week. Others say they think the operation is much smaller and similar in scope to the periodic search-and-destroy campaigns the Vietnamese have been launching this spring.

It is generally conceded that the Cambodians have proved to be formidable adversaries and masters of the same kind of guerrilla tactics that the Vietnamese Communist troops used against the Americans and South Vietnamese in the 60s and 70s. The Vietnamese have opted for the conventional warfare of tanks, artillery and heavy equipment which ties them to roads and necessitates vulnerable supply lines.

From the start, analysts say, the initiative has been with the Cambodians. By fierce hit-and-run attacks they have forced the Vietnamese to evacuate large areas along the frontiers. Chaudoc and Hatien, two small but once-flourishing towns along the border, are now virtually uninhabited.

The Cambodians have responded to Vietnam's frequent efforts to cool off the conflict with even greater ferocity. In March they answered a Hanoi proposal for a negotiated settlement with a multi-battalion attack on Hatien.

One analyst thinks Cambodia has decided on a policy of perpetual hostility toward its neighbor and former ally. He feels they apparently think that any rapprochement with Hanoi would lead to eventual domination by the more powerful Vietnamese.