WASHINGTON--The U.S. government failed to inform nuclear bomb factory workers after learning in the late 1940s that releases of radiation from the facilities posed serious health risks, according to a congressional report released yesterday.

The report, based in part on previously secret government documents, indicates that federal officials knew more about such health dangers than has been acknowledged, and that decisions were made to keep workers in the dark.

The report was prepared by the majority staff of the Senate Governmental Affairs Committee. The panel is investigating health research programs of the Energy Department, which owns the 17 major facilities that design and make nuclear arms.

More than 600,000 people have worked at the weapons plants over the last 45 years.

Sen. John Glenn (D-Ohio), committee chair, said in releasing the report that it "shows that the U.S. nuclear weapons program was exposing large numbers of workers to potentially dangerous health risks but did nothing to warn them."

The report focused mainly on the period of 1947 to 1954, during which the Atomic Energy Commission (AEC), the predecessor to the Energy Department, was rapidly expanding nuclear arms production amid deep suspicions about Soviet and other foreign work on nuclear bombs.

Records of an October, 1948 meeting of an AEC advisory committee indicated that enough was known then about releases of radiation at the Hanford plutonium plant near Richland, Washington, to raise concerns about workers' health. Yet it was decided at that meeting not to recommend closing Hanford temporarily while action was taken to stop the release of plutonium particles into the air.

The report deals almost entirely with worker exposure to airborne plutonium, but does note that significant quantities of the radioactive element were measured away from the Hanford plant.

A plant official said in a 1948 memo that "one of these samples" taken in Richland "was at least 10 times hotter than average."

Despite the concerns about health dangers, "a counter-balancing concern was the perceived need, fueled by Cold War fears, to continue plutonium production because of the relatively small size of the U.S. nuclear arsenal in 1948," the report said.

The report quoted a committee report from the 1948 meeting as saying, "there is no scientific evidence that it is an unwarranted hazard to continue the present process for six weeks, during which steps will be taken vigorously to control the hazard." The control measures apparently were not fully successful.

In December 1948, the manager of the federal Oak Ridge weapons plant in Tennessee recommended to the AEC's advisory committee that workers quitting the weapons program be told if they had exceeded the government's own daily radiation exposure limits and that medical aid be given if a former worker developed a radiation-related illness, the Glenn report said.

The advisory panel rejected the recommendation, the report said. Instead it recommended to the AEC that "a terminating employee should be advised at the exit interview as to the care that the AEC utilizes in protecting each employee."

The documents uncovered by the Glenn committee indicated that a major concern at the Hanford facility was the release of huge numbers of plutonium particles. The problem, dating at least to 1947, was traced to corroded fan duct work in the stacks of two chemical separation plants.

A March 1948 report by Dr. Herbert M. Parker, director of the Hanford health instruments department of General Electric Co., which ran the facility for the government, said an average of about 7.4 billion particles was being released from the two plants each month.

Parker wrote that "the critical hazard is to the inhalation and lung retention of particles," which he said "can produce radiation damage." At the time, it was estimated that a worker could be inhaling about 16 radioactive particles per month. This suggests that over a one-year period a worker could have inhaled an amount of plutonium that is more than twice the current official lifetime lung burden allowed for Energy Department workers, the Glenn report said.