The Occupational Safety and Health Administration announced yesterday that it would propose a tougher standard for worker exposure to benzene, a chemical known to cause a virulent form of leukemia in some workers exposed to high doses.

The unusual announcement of an upcoming regulatory action came in a series of telephone calls to reporters from Douglas Clark, press aide to OSHA Administrator Thorne G. Auchter.

The proposal won't be seen for months; Clark said the agency would announce by May 1 its formal intent to make a proposal.

In congressional hearings last month, Rep. David R. Obey (D-Wis.) noted that the agency had issued no new health standards since the Reagan administration took office, and accused Auchter of tilting decisions in favor of industry whenever possible. Obey said the administrator's decisions, which have resulted in the absence of any new regulation of such toxic chemicals as formaldehyde or ethylene oxide, failed to "give a benefit of the doubt, in the slightest, to persons asking for relief."

The Ralph Nader-affiliated Health Research Group, the Oil, Chemical and Atomic Workers Union and the Industrial Unions Division of the AFL-CIO have been preparing to petition OSHA for a tighter benzene standard, according to officials of two of the groups.

Benzene is a chemical widely used by the petrochemical and rubber industries. The current standard for benzene exposure, set in 1971, says that workers may not be exposed to more than 10 parts per million, averaged over an eight-hour day.

In 1977, OSHA issued an emergency standard reducing that by tenfold, to one part per million. The standard was made final in 1978, but never enforced; it was challenged in court and thrown out by the Supreme Court in 1980.

In its 5-to-4 ruling, the court said the agency had not shown that workers faced a significant risk at exposure levels below the 1971 standard, or that reducing the limit to one part per million would significantly reduce any risk.

Since that ruling, two OSHA scientists and a third from the National Toxicology Program of the Health and Human Services Department have developed a risk assessment, using data gathered in earlier studies, to estimate how many cases of leukemia could be attributed to workplace exposure to benzene.

That assessment, completed last September and published shortly thereafter, predicts that if 10,000 workers are exposed for one year to benzene levels of one part per million, between one and four will contract leukemia. By contrast, if 10,000 workers are exposed for 30 years each, an estimated 30 to 110 would contract the disease. A 1981 report by the National Toxicology Program estimates that up to 800,000 workers are exposed to benzene levels greater than one part per million.

OSHA spokesman Clark yesterday denied to the Associated Press that his announcement was designed to preempt the petition of the unions and the Health Research Group.

In an interview earlier this year, he said that, although the benzene risk assessment had been completed, the agency was waiting for an economic analysis before taking action.

Yesterday he said he didn't know if any such economic analysis had been completed.

John Martonik, deputy director of OSHA's Health Standards Program, said yesterday that his staff has been preoccupied with developing regulations on exposure to coal tar pitch, arsenic and workplace noise. "We just finished up some regulatory actions and we have the staff to work on [benzene] now," he said.