Former Prime Minister Harold Macmillan's government kept secret a 1957 accident at an atomic power plant that contaminated milk at an estimated 800 farms, according to official papers published Sunday.

The papers on the spring 1957 accident at the Wind-scale nuclear plant in Cumbria, northwest England, marked the first time full details have been made public.Government papers made public a year ago show that Macmillan also suppressed a report on another accident at Windscale in October of the same year. He feared shaking public confidence in the industry and jeopardizing collaboration with the United States, according to those papers.

The earlier accident contaminated milk with high levels of strontium 90, a deadly isotope found in radioactive fallout, according to Macmillan's private papers cited by The Observer, a London newspaper. The paper said the milk was sold to the public without any warning.

The Observer published extracts of the papers, which the Public Records Office released under rules permitting publication of selected confidential papers after 30 years.

Partial information about the accident was not released until 18 months later, the weekly paper said.

In a secret memo to Macmillan on Sept. 12, 1957, Agriculture Minister John Hare estimated "800 or more farms may be affected" by an escape of strontium 90 and that "the readings on some of these farms have been many times higher than the national average," the newspaper reported.

It said Hare also wrote that no action was being taken "to prevent milk being consumed or produced on farms in the area."

The paper quoted John Dunstan, a former director of the state-run National Radiological Protection Board, as saying full details of the amount of radioactivity released in the accident were not disclosed to the board until 1986. The release to that body came in connection with an inquiry into increased childhood leukemia near the plant, now known as Sellafield.

The newspaper did not report the cause of the accident and made no mention of any deaths attributed to it.

After the other accident in October, McMillan Macmillan suppressed a report on the causes, according to the papers released a year ago.

Sales of milk from an area measuring more than 200 square miles around the plant were banned after that release of radioactive.

The problem-plagued plant on the Irish Sea is one of the West's oldest commercial atomic power stations and largest nuclear reprocessing plants. It reprocesses used nuclear fuels from Britain and other countries to extract uranium and plutonium for making nuclear bombs.