ambodian resistance leaders opposing the Vietnamese occupation of their country charge that Hanoi is bringing up new stocks of chemical warfare substances for use against guerrillas along the Thai-Cambodian border.

Officers of the noncommunist Khmer People's National Liberation Front led by former premier Son Sann made the charge on the basis of intelligence they said had been gathered in the last few days by agents in Cambodia.

The front's military commander, Gen. Dien Del, said he was ordering his forces to make special efforts to come up with hard physical evidence of chemical warfare use, such as containers or ordnance, "to support the thesis of Gen. Alexander Haig."

Dien Del was referring to allegations this week by the U.S. secretary of state and State Department officials that a variety of chemical weapons, including deadly mycotoxins said in other accounts to be of Soviet origin, have been used against opponents of the Vietnamese-backed governments in Laos and Cambodia, as well as against rebels fighting the Soviet-installed regime in Afghanistan.

Various aspects of these charges are backed up to some degree not only by the Khmer People's National Liberation Front, but by the communist Khmer Rouge resistance, the Thai military, hospital sources along the border and Western diplomats. Up to now, however, no actual chemical warfare ordnance has emerged.

Hanoi and its protege government in Phnom Penh have denied the allegations. The Cambodian news agency called them "totally untrue," and the Vietnamese Army newspaper Quan Doi Nhan Dan charged the United States was trying to whitewash its own "crimes" during the Vietnam war.

In interviews at this camp in northwestern Cambodia near the Thai border, Dien Del and other front officials said Vietnamese in the past have used a knockout gas against the front's forces. Dien Del said he believed that another, lethal gas has been used against Khmer Rouge guerrillas.

The Khmer Rouge, who ruled Cambodia for nearly four years until ousted by Vietnamese troops in 1979, have long accused Hanoi of using chemical weapons. In April the Khmer Rouge charged specifically that 1,100 Cambodians had been killed during the previous 12 months by Vietnamese chemical weapons.

Officials of the Khmer People's National Liberation Front also have accused the Vietnamese of poisoning water supplies. But like the Khmer Rouge they have never been able of offer conclusive proof.

At the front-controlled Rithisen Camp straddling the Thai-Cambodian border about 15 miles south of here, camp official Thou Thonn said 17 persons had died from poisoning in May. He said doctors could not pinpoint the cause but that the deaths stopped after camp authorities closed 10 wells.

Thou Thonn and other officials said the last Vietnamese gas attack occurred at the nearby Nong Chan Camp in June. They said the Vietnamese used a nonlethal substance known locally as "combat gas," which incapacitates its victims for a few hours so that they can be captured, but leaves no lasting effects.

According to a State Department compendium, a similar incapacitant has been among the chemicals reported used by Soviet forces in Afghanistan.

According to Dien Del and other front officials, the effect of the gas can be countered by inhaling through a cloth soaked in ammoniac. When ammoniac is not available, the source said, other possible substitutes are urine or even crushed garlic.

Dien Del said he did not yet know what kind of chemicals were allegedly being moved up to the border area.

Citing an intelligence report received Tuesday by the commander of the Rithisen Camp, Dien Del said four trucks containing chemicals had left the Vietnamese-controlled city of Sisophon in northwestern Cambodia Sept. 13 and headed toward the border. He said the information came from a Cambodian loyal to the Vietnamese-installed Phnom Penh government who was captured by the front's forces.

In Bangkok, the head of Thailand's National Security Council, Squadron Leader Prasong Soonsiri, said he had received reports tending to substantiate Dien Del's claim.

In an interview, Prasong said a report received at the beginning of the month asserted that the Vietnamese moved 17 truckloads of chemical weapons from Phnom Penh to the central Cambodian city of Kompong Thom. He said some of the trucks more recently were driven to the western city of Siem Reap.

The Thai security council chief also said Vietnam had recently sent "a large number" of gas masks to western Cambodia for use by Vietnamese forces against guerrillas near the Thai border.

In response, the Thai Army has issued gas masks to its border patrols, an Army spokesman was quoted as saying Thursday. The spokesman added that the Army's chemical department had confirmed reports that the Vietnamese were using chemical weapons, but he did not elaborate.

Prasong said he agreed with U.S. reports that chemical weapons were believed responsible for serious illness and death among Hmong tribesmen in Laos. He indicated that Thai authorities had cooperated with U.S. representatives in a search for plant, soil and water samples to confirm the presence of toxic chemicals along the Cambodian border.

Prasong said he had approved a proposal to invite a United Nations panel to visit Thailand to investigate the claims about chemical weapons use.

According to foreign medical sources along the Thai-Cambodian border, doctors at some camps have reported treating victims of knockout gas.