Disease and malnutrition combined with a dropping birthrate are taking a greater toll of Cambodia's population than Communist executions, according to some of the latest analyses made here.

These assessments represent a major reversal in Western judgments of what has gone on inside Democratic Kampuchea, as the Communist government refers to the country, since the end of the war there 27 months ago.

Most Westerners who make an occupation of observing Cambodia from Thailand are talking in terms of several hundred thoudsand deaths from all causes.

This is a marked shift from the estimates of just six months ago, when it was popular to say that anywhere between 800,000 and 1.4 million Cambodians had been executed by vengeful Communist rulers.

The reasons for the huge variations in estimates are unclear, but may become more apparent when the U.S. House International Relations subcommittee on International Organizations hold hearings on Cambodia, beginning Tuesday.

A key witness will be CHarles H. Twining, a State Department officer who is considered by Western diplomats here to be perhaps the leading expert on post-war Cambodia.

But whatever the reasons, Cambodia watching is made extraordinarily difficult by the absence of written documents.

"Nothing but an occasional internal travel permit ever leaks out," said one observer. "They didn't write anything down during the war and they haven't changed. It's a government conducted by loudspeaker."

Recent changes in perception are thus based not so much on new intelligence as on reappraisals of earlier information carried into Thailand by many of the 25,000 refugees who have fled Cambodia since the war's end.

With the flow of refugees now almost dried up, observers in bangkok are re-examining the first wave of information more objectively. SOme concede that their first analyses were inflamed by horrifying tales carried by the refugees.

Not that I doubt for a minute that some of the most brutal excess ever perpetrated by man were conducted by the Khmer Rouge - and continue to be - but it's a question of scope," said a European diplomat who spent four years working in Indochina during the war.

"It now seems that perhaps no more than 200,000 were executed," he continued. "From what we know of the size of the Khmer Rouge armed force (currently estimated at about 800,000), the mechanics for executions on a more massive sale are just not there."

This diplomat and others interviewed along with independent Thai sources and medical specialists said they were convinced that malnutrition and disease, notably malaria, had taken several times more lives than executions.

A Southeast Asian diplomat, whose government has established relations with Cambodia but has not yet been permitted to send a mission to Phnom Penh, pointed out that even before the war spread to Cambodia in 1972, the country had high rates of infant mortality and deaths from malaria and related diseases.

But other Bangkok-based observers said they believed that many more Cambodians are succumbing to diseases today than before the war because of malnutrition.

The reason appears to be failure of the 1976 rice crop. The government averted famine in mid-1975 by evacuating Phnom Penh and othr cities and forcing almost every able-bodied person to work the land, but food production fell badly last year.

According to a U.S. photo satellite survey of the country, one Western source said, the area growing rice dropped between 25 and 50 per cent from 1975 to 1976.

Explanations vary. A Southeast Asian agriculture specialist said it happened because the Communists had instituted communal farming techniques, forcing the peasants to change their centuries-old methods.

"For example," he said, "by breaking up small family holdings into large paddy fields, they caused flooding in areas where it had barely been known before."

A Western European diplomat with years of experience in Indochina said he believed that most Cambodians were "just exhausted, pure and simple," and could not do as much as they had just after the war.

Onnpien Onnsamar, a refugee who escaped to the Thai border town of [WORD ILLEGIBLE] three weeks ago, lent support to this idea. A soldier in the U.S.-[WORD ILLEGIBLE] army of former President Loa Nol, he said he had survived by posing as a farmer in western Battambang Province.

They forced us to work until we know we had to run away or we would just drop dead," Onnsamar said.

Onnsamar said that for the last six months or so his daily rice ration had been cut to a measure of half a small condensed-milk can.

"To survive, we had to forage for bananas and other wild fruits," he said.

Some observers in Bangkok admit they are puzzled by the continuing reports of forced labor.

"At first, it seemed that the regime was going off-out to turn Cambodia into a mammoth rice-producing machine," said one Western diplomat. "That appears to have failed, and yet they haven't realized that there's nothing to be gained by working their people to death."

Another Western diplomat said his government had learned from contacts in Peking that the goal of the Cambodian rulers is to "recreate Angkortreference to the Khmer kingdom of Angkor, founded in 802 A.D., which reached its zenith in the 12th and 13th centuries.

Marked by its magnificent Angkor Wat and Angkor Thom Buddhist architecture at Siem Reap, 140 miles north of Phnom Penh, the Angkor civilization was built on the backs of vast numbers of slave laborers.

"In one way," said the diplomat, "they've recreated Angkor society already. They've established an elite which rules and everyone else is a bondsman. In the eitme of Angkor, the slaves built a pleasure dome for the benefit of a new powerful leaders. There's no pleasure in Cambodia today but the rest of the comparison is strong."

According to Westerners who have contacts in China and Vietnam, the Communist governments in those countries are alarmed and concerned by the conduct of the Cambodian leadership.

"What's going on in Cambodia today isn't communism," said one diplomat. "It's medieval."

Vietnamese antipathy for Cambodia has roots in the 17th and 18th centuries, when Vietnam annexed much of the Khmer empire. Although Cambodian Foreign Minister leng Sary was once rumored to have close ties to Vietnam, the relationship between the two Communist governments deteriorated quickly after the war.

China, however, carefully nurtured a number of leading Khmer communists, including Sary and Khieu Samphan, chairman of the State Presidium. China is one of nine Communist governments allowed to have embassies in Phnom Penh. In addition, several thousand Chinese advisers are working in Cambodia, particularly in Phnom Penh and the western provincial capital of Battambang.

One Bangkok-based ambassador said that his government's embassy in Peking has reported that the administration of Chairman Jua Kuo-Feng considers the Cambodian government "a monster created by the gang of four (the widow of Mao Tse-Tung and three other disagraced Chinese radicals)" and that China feels itself "stuck" with Cambodia.

Nothing that the Chinese appear to be ending Mao's massive forced population shifts, the envoy said the Chinese in Phnom Penh are attempting to "show the light" to the Cambodians.

"So far," he added, "they've had no luck, but they seem to think the Cambodians will learn in time that they've got to rejoin the world, at least to some degree."

To a very small degree, this process has begun. Through a purchasing agent in Hong Kong, the government has bought some U.S.-made DDT to combat malarial mosquitos and a shipment of powdered milk from Australia for a condensed-milk plant in Phnom Penh.

Some observers believe that the only possible explanation of Cambodia's self-isolation is that Samphan and othr members of the tiny ruling circle known as a angka "the organization," are aberrations of the Khmer character.

"If you look at these people you begin to perceive that they're atypical," said one student of Cambodian culture. "They were social deviates of one kind or another right after the start."

And although some leaders, loke Samphan, had extensive educational and other contracts with the former French colonialists, their experienced had apparently embittered them toward all Westerners.

Through his relationships with French Communists, Samphan apparently concluded that the only people needed in the new Cambodia would be those who contributed directly to society - farmers and workers. Middlemen of any kind were judged worthless. The doctoral thesis he wrote in Paris in the 1950s, which some observers think is the only plan for governing Cambodia today, makes this clear.

Few Cambodia-watchers believe that "the organization" is organized well enough to control much of the country. It is generally accepted that local military commanders, opeating from jungle bases, conduct their own small-scale border operations and impose summary justice.

But, according to one specialist, there does appear to be some flow of information along a chain of command.

"Once the word goes out, as it obviously did right after the war, that such-and-such a group is not psychologically adjusted to the new Cambodia, then the people on the ground do as they see fit," he said. "And if this means that all shopkeepers or teachers, or what-have-you are eliminated, then no one back in Phnom Penh is going to complain."