Vietnam and Cambodia exchanged bitter charges about the fighting along their disputed border yesterday following Phnom Penh's suspension of diplomatic relations.

Hanoi, however, also called on Cambodia to resolve their quarrel through negotiations. The appeal to Phnom Penh recalled the close ties the two Communist states had maintained during their common struggle against the United States earlier this decade.

The statement went on, however, to blame Cambodia for initiating the clashes - which Western analysts say actually began in the early 1970s before the defeat of the U.S.-backed governments in Saigon and Phnom Penh.

Hanoi's statement, which was broadcast by Vietnam Radio, said Cambodia had occupied large tracts of Gialaicong Province. Cambodian soldiers, the statement said, shelled many densely populated areas and the so-called New Economic Zones in rural areas, including some deep inside Vietnamese territory.

Cambodian raiderss, the broadcast said, committed "extremely barbarous crimes," such as disembowling pregnant women, butchering children massacring women and chopping off the heads of adults. "Many entire families were massacred with no survivor left," the radio said.

Earlier in the day, Cambodia's ambassador to Peking, Pich Cheang, held a press conference in which he denounced Vietnam's "aggression," saying that it was "similar to that of Hitler who invaded Czechoslovakia in 1939 in contempt of international laws, world opinion and morals." Vietnam, he said, was trying to force Cambodia into an Indochina federation and then swallow it up.

"Our only alternative is to fight," Pich Cheang said. Using the same terms as his government's communique that announced the break in relations, the ambassador attacked Vietnam's "repeated acts of aggression."

"There is no room for friendship" between the two countries, he said.

Questioned about the communique's reference to "foreigners" acting as "commanders and advisors" to the Vietnamese units, Pich Cheang said that he was not in a position to disclose their nationality.

Observers believe the Cambodians are trying to implicate the Soviet Union in Vietnam's policy. The Cambodian Communists have long resented Moscow's recognition of the U.S.-backed government in Phnom Penh up to its final days in the spring of 1975.

The ambassador ruled out the possibility of some third country serving as mediator in the dispute. He said "in accordance with our consistent policy," his government intended to solve the problem without help from other countries. He added: "To my understanding the government of Kampuchea [Cambodia] needs no mediation."

For several months China has been pressuring the two countries to reconcile their problems. Peking, however, has been handicapped by the fact that its relations with Vietnam have been strained since Hanoi's conquest of the South also in the spring of 1975, and the subsequent rise of Soviet influence in the Vietnamese capital.

In recent weeks, as the fighting grew in intensity, China has appeared to come down more strongly on Cambodia's side. It has printed several commentaries issued by Phnom Penh and Friday night New China News Agency reported the appeal by Cambodia Radio for its people "to defend the country," and stated that the Cambodians "can defeat any enemy any time."

Following Pich Cheang's press conference, a Chinese Foreign Minister official said "We regret this," making it clear that he meant the border clashes and not Cambodia's decision to break relations.

The Soviet Union remained silent yesterday on the Indochinese developments. Observers pointed out that there have been signs in recent weeks that Moscow was trying to repair its relations with Phnom Penh, citing as one example a magazine article praising Cambodia's foreign policy and denouncing Western criticism of the government's treatment of its population.

In Washington, a State Department spokesman said that the United States was following the dispute between Vietnam and Cambodia but would have no official comment to make.

At his meeting with reporters, Ambassador Pich Cheang said: "If the Socialist Republic of Vietnam respects Cambodia's territorial integrity and stops its aggression, negotiations may be carried or. Otherwise it will prove impossible."

A spokesman for the Vietnamese Foreign Ministry was quoted as saying his country seeks discussions and will "keep patient, understanding and calm while maintaining its natural right to defend its sovereingty."

In a dispatch from Hanoi, the Hungarian news agency MTI quoted the spokesman as saying that the border dispute is "an involved problem, a problem reaching back to the historic past, which the two sides should study and, in any case, discuss."

In Cambodia's original announcement of the break in relations, it said Vietnamese troops had attacked in the Parrot's Beak area in two pronvinces to the south and in two provinces to the north. In some cases they had penetrated as deep as 18 miles, the broadcast said.

It went on to quote from a speech by the Cambodian chief of state, Khieu Samphan, in which he accused the Vietnames ofplotting a coup d'etat against the Phnom Penh government. Earlier this year there were reports that the Cambodians had crushed an attempted revolt and executed the plotters.