Energy Secretary James R. Schlesinger has told federal occupational health officials that national security could be endangered if a proposed regulation is enacted cutting worker exposure to a suspected cancer-causing metal.

Officials said Schlesinger's warning was the first time the rationale of national security had been used to oppose costly production changes required of industry for worker safety.

In a two-page letter to Labor Secretary Ray Marshall, Schlesinger said a study by the Energy Department concluded recently that the cost of meeting a proposed exposure standard for beryllium may drive the only two non-communist producers of the metal out of business and cut off the U.S. supply.

"The loss of beryllium production capability," Schlesinger wrote in the Aug. 30 letter, "would seriously impact our ability to develop and produce weapons for the nuclear stockpile and, consequently, adversely affect our national security."

The Labor Department's Occupational Safety and Health Administration has proposed cutting worker exposure to the metal from two micrograms to one microgram in a cubic meter of air. The metal has been cited by federal health experts as responsible for causing fatal respiratory disease and cancer in workers.

A copy of Schlesinger's letter and other related documents were obtained by The Washington Post. The documents indicate that top Health, Education and Welfare Department officials, acting under political pressure, agreed recently to delay enactment of the tougher exposure standard and instead to institute a full review of the medical effects of beryllium.

The decision was made by Secretary Joseph A. Califano Jr., according to HEW documents, despite [WORD ILLEGIBLE] earlier from the department's senior medical officer that enough medical evidence already listed to determine the cancer [WORD ILLEGIBLE] of the metal to workers.

Federal health officials, who asked not to be named, said laboratory studies on the metal have provided unusually strong evidence of the metal's danger as a human poison and [WORD ILLEGIBLE] The metal has been shown to cause cancer, they said, in nine species of laboratory animals. Evidence in [WORD ILLEGIBLE] species is currently required by federal officials for a determination that a substance is a potential [WORD ILLEGIBLE]

In this letter to Marshall, Schelsinger said: "It is improbable that industry would invest millions of dollars in an attempt to reduce the beryllium exposure with no assurance that their facilities can be brought into compliance with the proposed standard."

Such a standard, Schlesinger added, places a heavy burden upon the free world's two primary bryllium producers, who might cease production of high purity beryllium metal and beryllium oxide" if the standard is put into effect.

The two firms producing the ultra-light metal are Kawecki-Berylco Industries Inc., of Reading, Pa., and the Brush Wellman Co., of Cleveland. Both have opposed the regulation since it was proposed two years ago. A 1975 federal study estimated that about 30,000 workers are exposed to beryllium dust and fumes on the job.

Beryllium is a critical component in the aerospace and nuclear industries and is used in items such as nuclear reactors, rocket motor parts, missile guidance systems and heat shields. According to industry officials, virtually all the pure beryllium that is produced is purchased for government use.

Concern over the toxcity of the metal is not new. In 1968, according to a HEW memo, officials became concerned over private researchers' warnings that the fallout from rocket firing could expose civilian populations near takeoff sites to beryllium. After a Massachusetts researcher threatened to make her fears public, a senior HEW official wrote, "This could be a bombshell if her views would ever get into print."

Other HEW documents obtained by The Washington Post indicate that intense political pressure this year caused the agency to back down from its strong stand for an immediate new beryllium standard.

In a letter in March, Dr. Julius B. Richmond, assistant HEW secretary for health, noted concern from political and industrial officials over the beryllium studies used by federal regulators. Richmond said he would go along with a review of the studies if necessary and estimated it would take two weeks.

"However," the HEW official wrote, in a letter to OSHA Director Eula Bingham, "our basic conclusions concerning the carcinogenicity of beryllium were reached before the above mentioned studies were completed. I would expect, therefore, that the standard-setting process can proceed."

Despite Richmond's assurances, HEW Secretary Califano came under pressure from several senators to delay the standard setting. In an Aug. 21 letter from Califano to Sen. John Glenn (D-Ohio), the HEW secretary noted the interest for an independent review of beryllium by Glenn - whose view of beryllium by Glenn - whose state is the home of one of the two beryllium producers and promised it would be undertaken by Richmond.

A spokesman for Califano said yesterday that the HEW secretary acted after Richmond apparently changed his mind and decided a new study of the metal was necessary. The spokesman said Califano discussed the beryllium situation with Richmond but that Richmond apparently did not tell his boss of his earlier letter to Bingham saying the new study was not necessary.

Califano's review, according to HEW documents and federal officials, is considerably broader than the one first suggested. Federal officials estimated it could delay implementation of the beryllium standard for up to a year. The standard was scheduled to go into effect during the past summer, officials said.

Califano was asked about the beryllium controversy during a union health and safety conference here this week. He told delegates to the conference he was not aware of the conflict over the exposure standard for the metal.

Schlesinger's letter has raised additional questions. Energy Department officials said yesterday it would cost about $150 million to convert the nation's two beryllium producers' facilities to attempt to meet the proposed standard.

However, according to Dr. F. Charles Gilbert, deputy director of DOE's Office of Military applications, only a small portion of the two firms' total beryllium production is the type purchased by the government.

Gilbert said about 2 percent of Kawecki-Berylco's beryllium production is "pure beryllium," the kind used by the government for defense and aerospace programs. About 10 percent of Brush Wellman's output is pure beryllium, he said.

An official of Kawecki-Berylco estimated yesterday it would cost his company about $12 million to try to meet the new standard for its pure beryllium production facility. Brush Wellman officials said they were unable to estimate the cost of trying to convert their pure beryllium facility.

Officials of both firms said, however, they did not believe they could meet the proposed standard with current technology no matter how much money they spent, H.G. Piper, president of Brush Wellman, said in a telephone interview his company would continue its nongovernment beryllium production even if it meant violating the new standard.

"We already violate the standard they have now," he said.