Industry and union officials said yesterday the Energy Secretary James R. Schlesinger vastly overestimated the cost of meeting a proposed safety standard for U.S. workers exposed to the suspected cancer-causing metal beryllium.

In an unprecedented effort to halt implementation of a proposed federal exposure standard for a carcinogen, Schlesinger wrote Labor Secretary Ray Marshall in August and said the cost of meeting the standard was so high it could cut off the supply of the metal and endanger the national defense. A copy of Schlesinger's letter was made public this week by The Washington Post.

Union officials and a spokesman for one of the two U.S. manufacturers of beryllium said in separate interviews yesterday that schlesinger's estimate of $150 million to meet the proposed standard was wildly high.

A senior official of Kawecki-Berylco Industries Inc., a Reading, Pa., firm that manufacturers the metal at in Hazleton, Pa., plant, said the cost of refurbishing the facility to try to meet the proposed standard would actually be about $4.6 million. On Wednesday he put the figure at $12 million but he said yesterday that figure was incorrect.

The Occupational Safety and Health Administration has requested a cut in the exposure level for some 30,000 persons who work with beryllium from two micrograms to one microgram in a cubic meter of air. The Kawecki-Berylco official said that even if his firm did spend $4.6 million, however, he did not believe it could meet the new standard with the technology available today.

Spokesmen for the Oil, Chemical and Atomic Workers Union, which represents workers at the plant said the plant was underutilized and could accommodate all the government's requirements for the critical ultra-light metal. The Kawecki-Berylco official also saiy yesterday "We don't know how much we could raise production but the plant certainly was designed for a much larger capacity than it now has."

Energy Department officials said they were surprised yesterday when they were informed of the union and industry figures.

"Something is very wrong," said Dr. F. Charles Gilbert, deputy director of the department's Office of Military Applications. "We will have to to go back and check our source of information to see how we arrived at our figure for this."

Meanwhile, both Marshall and Health, Education and Welfare Secretary Joseph A. Califano Jr. indicated yesterday they would not hold up implementation of the standard.

Documents obtained by The Washington Post this week indicated that Califano overruled his own senior medical adviser in August and ordered a full review of the medical data on beryllium, a move that federal health experts estimated would hold up implementation of the standard for up to a year.

In a statement Califano said yesterday he had not been aware of the details of the beryllium situation in August and that he had requested a full briefing on the subject in the next 10 days. "Whatever action we take subsequently will be completed promptly," he said.

In a separate statement Marshall called beryllium "one of the most toxic substances known to man." He said the OSHA law allowed a national defense exclusion from the proposed standard but he added, "We don't think a new standard will jeopardize a national defense effort."