The Reagan administration is preparing to force chemical firms to label their products to protect workers, with the fervent support of the same industry that once spurned the proposal as unnecessary and too expensive.

The chemical industry has decided it would rather be governed by Uncle Sam than by dozens of state and local laws.

Labor Secretary Raymond J. Donovan is expected to give the go-ahead soon to the Occupational Safety and Health Administration's "right-to-know" rules. The rules would require more than 300,000 firms that make, import or process chemicals to tell employes what they are working with and what the chemicals' hazardous properties are, at a startup cost estimated by OSHA at $604 million.

As described in the draft proposal on Donovan's desk, the rules would be narrower and far less costly than the ones that were hastily proposed by the Carter administration four days before leaving office in 1981, and just as quickly shelved by President Reagan's regulatory relief team.

The Carter proposal covered far more industries and workers, but also carried a first-year price tag of $2.6 billion.

The Reagan proposal is unlikely to please organized labor, which contends that OSHA's rules, designed to cover only manufacturing businesses, will leave more than 80 percent of American workers in the dark. OSHA says its rules will cover 8.9 million workers. According to the AFL-CIO, 60 million workers will be left unprotected.

But the chemical industry hopes the rules will be just broad enough to squelch a spate of state and local "right-to-know" laws that have sprung up while the federal rules languished. A dozen states and a half-dozen cities have enacted their own chemical labeling requirements, and more than a dozen other states are considering similar laws.

Some of the state laws go far beyond even the Carter administration's proposal. New Jersey, for example, recently adopted the toughest labeling law in the nation, which requires industry to label all its substances--hazardous or not--and supply the information to community groups and health officials, as well as to workers.

Faced with the administrative nightmare of complying with all the state rules, the chemical industry has virtually begged OSHA to get the federal rules back on track.

"Without a strong federal role, individual states will enact a variety of diverse labeling rules that would hamper interstate business operations and impede worker protection," the National Paint and Coatings Association pleaded in written comments to the agency.

The association's comments were seconded vigorously by a number of chemical firms, including E.I. duPont de Nemours & Co., American Cyanamid Co. and Dow Corning Corp., which worried that attempts to comply with a variety of state laws might result in "excess information on a product label."

Whether the new rules will supersede all state laws is likely to be a matter for the courts to decide, according to Mark DeBernardo of the U.S. Chamber of Commerce, which also supports the federal proposal. But DeBernardo said the Chamber hopes that OSHA's rules will have at least a "chilling effect" on states that have not yet passed labeling laws.

"They would feel no pressing need," he said.

AFL-CIO official Peggy Seminario sharply disgreed. "The bottom line is that workers want this information," she said, "and the fact that industry and the Office of Management and Budget collaborate and try to provide minimal information isn't going to stop them from wanting it."

OSHA chief Thorne G. Auchter called the proposed rules an "excellent piece of work that will be of tremendous help to working men and women."

But some other OSHA officials agree with labor. "The information just goes from prince to prince," said one agency official, who asked not to be identified. "The data goes from the manufacturer to the user, and not out to the public or the worker."