The Office of Management and Budget last week dealt another blow to the Labor Department's proposed work-place controls for the toxic chemical ethylene dibromide, disapproving proposals for medical testing on some exposed workers because "it is not clear how these tests will reduce the cancer incidence of EDB exposure."

Medical testing, designed to monitor exposed workers for early signs of disease and to provide epidemiologists with more information about the effects of a hazardous substance, is a basic component of several existing and proposed Occupational Safety and Health Administration standards, including those governing vinyl chloride, lead and asbestos.

Ethylene dibromide (EDB) is used in small quantities as a citrus fruit and grain fumigant and a gasoline additive. OSHA estimates that about 56,000 workers, many in the food-handling and food-transportation industries, are exposed to the chemical.

OSHA has been under increasing pressure to develop a more stringent standard for exposure to the chemical since recent reports were published indicating that the cancer risk from it, even at legal limits, was very high. But OSHA's attempts to publish a stricter standard frequently have run into roadblocks from the OMB.

Last month, OMB director David A. Stockman called Labor Secretary Raymond J. Donovan and persuaded him to withdraw a proposed EDB rule because the OMB had not approved it under the regulatory review process instituted by President Reagan in 1981.

Soon thereafter, the OMB gave its approval and the proposal was published, but the incident left more than a residue of bad feeling between the two agencies.

The new OMB objection to the medical testing requirements is based on a 1980 law giving the OMB the right to screen new paper-work requirements imposed by executive branch agencies. Because many rules involve some monitoring or record-keeping, the law gives the budget office considerable latitude in affecting the government's attempts to regulate.

In this instance, medical monitoring becomes a "paper-work" requirement, and OSHA must satisify the OMB that the paper work is needed.

OMB official Arnold Strasser, who heads the agency's paper-work review efforts, said Friday: "We're saying there is considerable question in our mind, and no final answers . . .about the need, burden and use of doing this thing."

Strasser indicated he was aware that other OSHA rules have similar testing requirements, and he did not clarify whether his agency's questions centered on the selection of workers to undergo the tests or were directed more broadly to the usefulness of any medical monitoring of workers exposed to hazardous chemicals.

On an agency work sheet, OMB desk officer Nancy Wentzler wrote that "a major problem is the vast set of medical tests that are required for workers exposed to one-half of the proposed exposure limit for over one month per year or who wear respirators. It is not clear how these tests will reduce the cancer incidence of EDB exposure."

OSHA spokesman Susan Fleming said Friday that her agency had not been informed officially of OMB's objections, but she said OSHA officials do not expect any delay in the final rule.

Such medical testing, she said, has "always been a part of OSHA's health standards as required by the Occupational Safety and Health Act . . . . We are confident OMB's concerns can be resolved."