A dissident faction of the Khmer People's National Liberation Front, the largest noncommunist resistance group fighting the Vietnamese occupation of Cambodia, announced today that it was the "sole master" of the organization in a virtual military coup against its leader, Son Sann.

In response, Son Sann issued a statement denouncing the "open rebellion" of the dissident group, called the Provisional Central Committee of Salvation. He said the organization was "illegal" and henceforth "banned," and he called on the guerrilla group's fighters and adherents to tighten ranks behind him.

The front reportedly has received funding from the CIA and it is an intended recipient of $5 million in overt aid under legislation sponsored by Stephen J. Solarz (D-N.Y.) that passed last year.

The faction's statements appeared to dash chances of healing an open rift in the Khmer Liberation Front's leadership following months of internal bickering. The rift became public last month when the Provisional Central Committee of Salvation was formed under the leadership of the front's military chief, Gen. Sak Sutsakhan, who accused Son Sann of exercising "dictatorial powers" and meddling in military matters.

The squabbling within the ranks of the noncommunist Cambodian resistance has coincided with an upsurge in activity by the communist Khmer Rouge, the most powerful member of a three-party coalition battling the Vietnamese in Cambodia.

In a statement broadcast today, the Khmer Rouge said its widely reviled leader, Pol Pot, would cease all military and political activity when Vietnam signed an agreement to withdraw its troops from Cambodia under international supervision. The Khmer Rouge said the pledge was a response to Vietnam's offers to withdraw its occupation troops, estimated to number 160,000 to 180,000, in return for the "elimination" of Pol Pot. But diplomatic observers doubted that the pledge would be taken seriously in Hanoi.

The Khmer Rouge announced in August that Pol Pot had "retired" as military commander of the Khmer Rouge.

The Khmer Rouge appear to have been gaining strength inside Cambodia compared to the two noncommunist resistance groups. This has intensified concerns about the dispute within the front. The aim of the United States and noncommunist nations in Southeast Asia has been to build up the front and a group headed by Prince Norodom Sihanouk, the Armee Nationale Sihanoukienne, to counterbalance the Khmer Rouge and enhance the resistance coalition's international standing.

In its statement distributed today, the Provisional Central Committee of Salvation declared that "the polemics between Mr. Son Sann and his partisans and the committee have lasted long enough." If allowed to persist, it said, the dispute could create "harmful confusion" among fighters and "those friendly countries which support us."

The statement, signed by Gen. Sak Sutsakhan, said the committee was "the sole master of the situation, exercising full control over the Khmer People's National Liberation armed forces and over the civilian administration."

One of the prime movers behind the committee, Abdul Gaffar Peang-meth, said it would now turn its full attention to the military struggle inside Cambodia. Asked about the role of Son Sann, he said, "We are going to ignore him."

Gaffar, who was expelled from the front last month by Son Sann for "insubordination," said the committee included Gen. Dien Del, the group's top field commander, and former prime minister of Cambodia Huy Kanthoul.

The front's "general staff is with us" and local units are being warned to obey the committee's orders, said Gaffar. "We are not going to allow anyone to get out of line. This is army discipline."

A Son Sann supporter, Sangwar de Lopez, acknowledged tonight that the rebels appeared to have the support of the military hierarchy, but he said a majority of local commanders, rank-and-file guerrillas and civilian followers continued to back Son Sann.

Independent reports from the Thai-Cambodian border, where nearly 250,000 Cambodian refugees are encamped, also indicated that sentiment among civilians was running in favor of Son Sann, 74, who also serves as prime minister of the resistance coalition.

De Lopez, the front's representative in Washington, denied here that Son Sann had been meddling in military affairs. He said the leader merely had wanted to know how foreign aid to the group was being used by the guerrilla commanders.

With talks between the rival factions having broken down, a resolution of the dispute now is seen as largely dependent on the attitude of resistance backers, notably Thailand. Thai authorities control the flow of aid to the resistance and have increased their influence over it since the Vietnamese wiped out guerrilla bases on the Cambodian side of the border last year.

The Thai government has avoided public comment on the dispute, but Son Sann supporters said they suspected Thailand was promoting the rebels. They said the Thai military has not allowed Son Sann to visit the border, blocking plans to rally his supporters.