Carter administration officials yesterday blamed Cambodia's Communist rulers for one of the world's worst continuing tragedies of disease and hunger, after a surge of political executions following the American departure in April, 1975.

"Most reports are that executions continue," but "the number who died from disease or malnutrition is greater than (from) executions," said the U.S. Foreign Service's chief Cambodian watcher, Charles H. Twining, Jr., 35.

Twining, just returned from Bangkok, Thailand, and Assistant Secretary of State Richard C. Holbrooke, told a House International Relations subcommittee headed by Rep. Donald Fraser (D-Minn.) that it is impossible to given any "precise figure," or even an accurate estimate on the deaths in Cambodia.

Some "journalists and scholars," Holbrooke said, "guess that between half a million and 1.2 million have died since 1975." The only thing officials can say with confidence. Holbrooke said, is that "the number of deaths appears to be in the tens if not hundreds of thousands."

Some published accounts attribute the disputed estimate of 1.2 million or more deaths to "American embassy sources." Twining disclaimed that estimate in talking with reporters, as do other U.S. officials. No figures on Cambodia "are worth very much," said Holbrooke. Cambodia's population is similarly disputed; figures range from 5 million to 7.7 million.

Nevertheless, Holbrooke said. "Based on all the evidence available to us, we have concluded that Cambodian authorities have flagrantly and systemically violated the most basic human rights."

"They have ordered or permitted extensive killings," he said, "forcibly relocated the urban population: brutally treated supporters of the previous government, and suppressed personal and political freedoms."

Holbrooke said that "my guess . . . is that for every person executed, several have died of disease or malnutrition or other factors, which were avoidable if the government itself had not followed the kind of policy. . .which seeks to completely transform a society by applying purely draconian measures."

After hearing the witnesses, the subcommittee approved a resolution for House action deploring "the continuing disregard for basic human rights including atrocities and killings of the Cambodian people by the government of Democratic Kampuchea."

The resolution calls on President Carter to cooperate with other nations, through such forums as the United Nations to end "flagrant violations of internationally recognized human rights in Cambodia.

Deleted from the resolution, as it was originally introduced by Rep. Stephen J. Solarz (D-N.Y.), was any reference to the major U.S. involvement in Cambodia during the Indochina war, which was barely alluded to in the hearing.

In its original form, the resolution said. "The United States must recognize its responsibility as a constributor to the disastrous events which have taken place in Cambodia . . ."

Former President Nixon's decision to send U.S. troops into Cambodia in April, 1970, to attack North Vietnamese troops after Cambodia's ruler Prince Norodom Sihanouk was overthrown by a coup provoked an American uproar. There were protects and defections inside the federal bureaucracy, and violent demonstrations swept college campuses with the slaying of students by National Guardsmen at Ohio's Kent State University.

In the subsequent spread of warfare across Cambodia, the American backed government of Cambodian Premier Lon Nol was overwhelmed by suddenly expanded Khmer Rouge forces, who now rule Cambodia.

This history was passed over in yesterday's hearing except for fleeting allusion to it. In a hearing before the subcommittee last May, there were angry exchanges between Solarz and a private Indochina specialist, Gareth Porter.

Porter charged that the subcommittee was ignoring the American record in Cambodia.He said it was "a myth" that "1-to-2 million Cambodians have been the victims of a regime led by genocidal manicas," Porter claimed that an unsubstantiated "bloodbath" version of Cambodia was nourished by a Reader's Digest book, "Murder of a Gentle Land," by John Barron and Anthony Paul, and another study by a French priest, Francois Ponchaud, "Cambodge, Annee Zero" ("Cambodia, Year Zero").

Twining's testimony yesterday, inlike those two accounts, avoided all countrywide numbers. Twining stressed that accounts from Cambodian refugees, the core of information on present-day Cambodia, are largely limited to one section of the small nation, the northwest, and come from refugees reaching Thailand.

Therefore, Twining said, "we can't even estimate how many have been executed."

However, Twining testified, that after systematic killings in 1975 of Cambodians associated with the Lon Nol government, in early 1976 killings began of "all other intellectuals."

Twining said "an intellectual was anyone who had a seventh-grade education or above." When asked if that was documented, Twining said "this was my own deduction," based on interviews with hundreds of refugees.

After the initial killings by shooting, he said, the most common method of execution "was to hit the people on the back of the head with a hoe handle or an axe handle," as though to save ammunition.

Twining said "I have never heard of one trial" in Communist-ruled Cambodia. As one example of the death toll, he said that in a village of 1,200 persons, during one year there were 15 "military types taken away and presumably executed," about an equal number of civilians similarly removed: "perhaps 50 older people died of disease," and 80 children died of disease of malnutrition.

Twining emphasized that "our knowlegde is so superficial," however about the government of Cambodia. "Khmer Rouge on a local level," he said, "admit they don't know who is in charge."

There is an "inner circle" politburo of five members, Twining said, but the head of state, Khieu Samphan, is not in that inner group, but in an "outer circle" of another five officials, the leader of the inner group is believed to be Saloth Sar, Secretary general of the Cambodian Communist Party, whose existence is not admited.

An earlier witness told he subcommittee that Pol Pot, the identified premier of Cambodia, is believed to be a pseudonym for Saloth Sar.

Cambodian lacks a school system as such, Twining said, although it appears to have "some technical schools." The nation is also said to have no money system.

Diplomatic missions in Cambodia are limited to China, Cuba, Albania, North Korea, VIETNAM, Laos, Romania, Yugoslavia and, one non-Communists nation, Egypt. Twining said that diplomats are severely restricted in the capital, Phnom Penh, except for the Chinese, the strongest foreign presence in Cambodia.

Cambodia's rulers are so determined to isolate themselves. Holbrooke noted, that they recently rejected an interest-free loan from the Organization of Petroleum Exporting Countries.

Although no direct mention was made in the hearing that Cambodia's rulers list in the United States as their No. 1 enemy, Holbrooke told the subcommittee there is virtually no prospects that the United States can influence Cambodia.

The only indirect U.S. action permitted so far, he said, was authorization for a private organization to send DDT insecticide to Cambodia for malaria control.

Cambodian authorities, Holbrooke noted, "claim that only two or three thousand died during the evacuation of Phnom Penh after the Khmer Communist takeover and as many again during the first months in the countryside."

Ieng Sary, Cambodia's deputy premier in charge of foreign affairs, told an Italian interviewer in report published last May that "the Khmer revolution has no precedents." He said the country was being reconstituted on an agricultural basis, with its cities reduced "to human dimensions" but "it is still too early to announce what we are doing in our country."

Those who claim that Cambodia has executed hundreds of thousands of people, he said, "are crazy. Only hardened criminals have been sentenced."

Subcommittee Chairman Fraser, at the close of yesterday's hearing, alluding to U.S. policy toward Cambodia during the Indochina war, which he opposed, said he cannot agree that the past record "now disables us from speaking out."

Rep. Michael Harrington (D-Mass.)., said he wished the hearing had recorded "comparatively greater concern" about the Cambodian history in which we were directly involved." Holbrooke said "I share your feelings about that policy" but he said. "We cannot let it be said that by our silence we acquiesce in the tragic events in Cambodia."

A dissents in defense of the Nixon adminstration record came from Republication Edward J. Derwinski (Ill.). He said, "I think our motives were good, our actions and policies basically sound." The fault, he maintained, was the refusal by Congress to sustain a continuing American role in Cambodia.

The only prospect that Holbrooke held out for U.S. action involving Cambodia "is to continue our assistance to refugees who have fled Vietnam, Laos and Cambodia."

However, he acknowledged that plans to admit an additional 15,000 Indochinese refugees to the United States would bring in only about 750 Cambodian refugees. The criteria give higher priority to Vietnamese refugees.

Twining said there are about 11,000 Cambodian refugees in Thailand. The flow of refugees has been sharply reduced, he said, by a "scorched earth policy" on the Cambodian side of the border, which includes minefields.

Only about one out of five persons who tries to flee Cambodia to Thailand, Twining said, survives the escape. By contrast, he said, many Cambodians flee across the less-guarded border to Vietnam, and he said "generally they are being well-treated." Vietnam and Cambodia, Holbrooke noted, have "400 years of hostility."