Many hundreds of thousands of people have perished in Cambodia directly or indirectly as a result of the policies of the Communist government that came to power there in 1975, according to a British government report released yesterday.

The report cited "reputable observers" for this estimate.

It spoke of widescale executions, forcible evacuation of cities and complete suppression of the Buddhist religion.

There have been a number of charges of widespread executions in Cambodia, but the Cambodian government, in a note to the United Nations last April, said it had taken action only against a "handful of traitors." It criticized Britain for demanding action on alleged human rights violation in Cambodia.

The British government report, released by the Foreign Office made these allegations:

1. Since April 1975 thousands of refugees have fled Cambodia, following a radical upheaval which had involved the "forcible evacuation of the cities, widescale executions, and the destruction of much of the traditional . . . way of life."

2. There were widespread executions of military officers of the former government after the Communists came into power. "It is clear from many accounts from different sources that the execution of officers of the former Khmer Republic's army was . . . a calculated act of policy," the report said.

3. Most senior officials who "disappeared" in 1975 have not been seen again.

4. Father Francois Ponchaud, a French authority on Cambodia prepared a report drawing on the evidence of 40 Cambodian refugees from eight Cambodian provinces, all of whom left their country in 1977. This provided evidence that the executions were continuing on a considerable scale in 1977, the British report said.

5. No refugee and no official Cambodian statement has ever mentioned a trial. There were no courts, no defense and no appeals. Refugees frequently reported that laziness or the mere expression of a complaint about the conditions of life was sufficient grounds for execution.

6. It has been estimated that at least 85 percent of the population of Cambodia used to practice Buddhism, which was the state religion. In the past three years however, Buddhism has been completely suppressed, the British report said.

7. Families have been divided and it has been general policy to separate men from women.

8. The report said Fr. Ponchaud gave it as his view in February 1978 that the estimate that more than 100,000 Cambodians had been executed must be taken as the absolute minimum. It is possible that two or three times as many people have been executed. The number who died because of the lack of food and of medical and sanitary facilities, and from the frantic pace of work, might well have been more than two million. He added that he had reports of villages in which a third, a half or even nine-tenths of the population had died.