Cambodian Premier Pol Pot has escaped to the hills of his country where he is commanding a guerrilla war against the Vietnamese invaders, U.S. sources said yesterday.

Intelligence analysts are predicting that the war will last a long time, largely because both sides have plenty of guns and ammunition for the type of hit-and-run warfare being waged.

The People's Republic of China has already started running in war supplies to Cambodian forces, the officials said, while the Soviet Union so far has limited itself largely to trying to find out what is going on in this newest Indochinese war.

The Soviet fleet now off Vietnam is more heavily equipped for electronic eavesdropping than for fighting, according to well-informed officials.

The prospect of China and the Soviet Union getting more embroiled in the war in Cambodia provoked a fresh expression of concern from the State Department yesterday after Vietnam charged that a small contingent of Chinese troops attacked a Vietnamese post on the border.

"We would be seriously concerned over a Chinese attack on Vietnam," said State Department spokesman Thomas Reston.

"We want an end to the present fighting and tension. We do not want any escalation, and we are seriously concerned that the continued combat between Vietnam and Kampuchea (Cambodia) can lead to an extended conflict."

The alleged Chinese attack even if it was as large as Vietnam claimed, was still a skirmish, U.S. intelligence officials stressed yesterday in discouraging speculation that either China or the Soviet Union has involved its forces in a big way.

Vietnam, in a broadcast monitored in Hong Kong, charged that "a company of well-armed soldiers" -- about 100 men -- from China attacked a Vietnamese border post in Lai Chau Province, killing three defenders, wounding six and kidnaping four others.

U.S. sources with the latest intelligence said Cambodia is organizing its forces for protracted guerrilla warfare. The Vietnamese command is now confronted with the same hard choices that faced the American command in South Vietnam in the 1960s, officials said.

The Vietnamese, opposed by guerrillas who are gaining strength, have three options, as U.S. military leaders read the situation: dig in for a long war, escalate in hopes of winning decisively, or withdraw.

The Vietnamese, like the Americans before them, are fighting on strange ground at the end of a long supply line against native troops supplied by a major power.

The Cambodians, sources said, are making classic hit-and-run guerrilla raids.They are blowing up bridges and attacking isolated Vietnamese units, while avoiding stand-up battles with the heavier armed invaders.

U.S. intelligence has obtained hard evidence, sources said, that Pol Pot is alive in the Cambodian hills. He is credited with exercising some command over the scattered Cambodian forces, but how much is not known. Presumably, U.S. intelligence learned of Pol Pot's whereabouts through electronic intercepts or reliable agents.

China is sending Cambodia war supplies overland through Thailand, by aircraft landing at remote strips in Cambodia, and by sea, sources said.

Since the traffic through Thailand must be kept to a trickle to be tolerated by the government there, sources predicted that Chinese freighters laden with war supplies will steam into the Gulf of Thailand. Cambodian sampans, which have been bringing in some war supplies, would then unload the Chinese freighters, depositing the supplies on remote beaches at night.

Prince Norodom Sihanouk, former head of Cambodia, in an interview printed in The New York Times yesterday, quoted Teng Hsiao-ping, Chinese vice premier, as telling him that Thailand had agreed to let its ports and land routes be used for Chinese war supplies destined for Cambodia.

If Chinese merchant ships should sail into Cambodian or Thai ports, as some analysts are predicting, the next question is what the Soviet ships off Vietnam would do.

The United States, confronted with the same decision when foreign freighters took war supplies into North Vietnam's harbor of Haiphong in the 1960s, did not interfere at first. Finally, however, the United States mined the harbor.

Right now, sources said, the Soviets have little firepower in their task force standing off Vietnam. The most lethal warship is a Kresta-class cruiser of 7,500 tons. It is armed with anti-aircraft and antisubmarine missiles.

Most of the ships in the Soviet task force are trawlers and others equipped for eavesdropping on Vietnamese radio communications.

One high-ranking U.S. military officer assessing the Soviet naval presence off Vietnam said yesterday that the Soviets themselves probably do not know what to do with their task force.

"This idea of showing the flag with a blue-water navy is new for them," he said of the Soviets.