Vietnamese troops are pushing toward the eastern shore of the Mekong River in an apparently well-coordinated attempt to slowly dismember Cambodia, according to analysts here.

The move toward the river town of Kratie, one of a series of key actions in the last several days, has revealed what appears to be a long-term strategy for installing a pro-Vietnamese government in Cambodia, beginning with the creation of a "liberated zone" in the eastern part of the country.

The push north toward Kratie, combined with the threat of a similar Vietnamese move south from Laos, puts the forces of Cambodian Premier Pol Pot in a serious squeeze, despite the lack of an immediate threat to the capital at Phnom Penh.

The Pol Pot government, having reportedly lost a bloody battle near the Vietnamese border last week, has become impressed enough by the new threat to issue an unusual public call for help.

According to one report, the Phnom Penh leaders have also begun to prepare plans to evacuate the capital and join a guerrilla war if the Vietnamese forces come too close. Analysts here say they doubt Hanoi has any immediate plans to move on Phnom Penh. "There's nothing there worth taking, anyway," one analyst said.

Instead, the Vietnamese seem determined to make up for earlier unsuccessful clashes with the nationalistic Cambodians by putting steady pressure on the country's southeastern border with Vietnam and northeastern border with Laos, a client state of Hanoi. Analysts say there have been significant movements of Vietnamese forces into southern Laos.

By some estimates, up to 25,000 troops may now be poised there to draw part of Cambodia's outnumbered army north. With the southeastern part of Cambodia threatened by another 100,000 Vietnamese troops, Cambodian regular troops may be forced to abandon the rest of northeastern Cambodia to a newly organized anti-Pol Pot National Front, which is expected to begin setting up liberated zones east of the Mekong.

Cambodian troops near the town of Snuol in the so-called Fishhook salient, a piece of Cambodian territory jutting into Vietnam, suffered a serious defeat last week as intense fighting resumed after another rainy season lull in the year-old conflict.

Several hundred Cambodians were reportedly killed, injured or captured. For at least two weeks the Vietnamese have been conducting heavy air strikes in the area, using American-made F105 and A37 fighters captured in the collapse of the U.S.-backed Saigon regime and Soviet fighters provided by Hanoi's allies in Moscow.

The official news agency of Cambodia's most important ally, China, released Thursday the text of an appeal from Cambodian President Khieu Samphan for international "opposition to Vietnam's acts of interference, intervention, aggression and annexation against Democratic Kamphuchea," as the Cambodians refer to their country. The news agency said the letter had been sent to the "governments of friendly countries," but did not name them.

Analysts said they thought some of the message had a ring almost of desperation. The Pol Pot government has invited a number of Western correspondents to visit the country this month, in an effort to win international support and combat criticism that it has sanctioned a bloodbath.

China's nominal head of state, Yeh Chien-ying, repeated Peking's support of the Pol Pot government in a reply to the letter. But analysts remain uncertain how far the Chinese are willing to go to support Phnom Penh beyond the large stock of arms and military advisers they have sent.

Analysts here said the clearest sign of a coordinated Hanoi plan to squeeze Pol Pot out of power came with the Vietnamese announcement of a Cambodian National United Front for National Salvation.

The organization, operating with Vietnamese sponsorship, said it was composed of anti-Pol Pot Cambodians operating "somewhere in the liberated area. It announced a program emphasizing family life, free choice in marriage and an eight-hour work day, a significant appeal to Cambodians whose families have been broken up and have been forced into all-day labor in what is now a barter economy.

Foreign observers have assumed that there is widespread opposition to Pol Pot, who has ruled in large part by killing off his political opponents and groups like teachers and former pro-Western army officers who might lead future revolts.

Cambodian troops, however, have fought fiercely and with high morale against the Vietnamese, an age-old enemy of Cambodia's Khmer people. The appeal by the new insurgent group, no matter how much it may influence disenchanted Cambodians, may not be heard by many of them because radios are banned.

Analysts here say they do not consider any one town, even Kratie, a former capital of the pre-1975 communist insurgency, to have unusual strategic importance in a country that has been broken down into so many self-supporting farm areas. The Vietnamese assaults, which appear to involve an estimated 20,000 troops, would open up areas for the anti-Pol Pot insurgents to set up their own local governments, creating a base for an eventual move west and south toward Phnom Penh.

According to a broadcast by the insurgents, the president of the Front, Heng Samrin, 44, joined the communist movement in 1959 and in 1976 was political commissar and commander of the 4th Division and deputy chief of the military zone bordering Vietnam. None of the 14 members on the Front's Central Committee, including people identified as army officers, intellectuals, peasants, trade unionists and Buddhist clergy, are nationally known. Analysts assume many are linked to a pro-Hanoi wing of Cambodia's Communist Party who were purged after the victory over the U.S.-backed Lon Nol administration in 1975.