Boston — Weaving his way past a detached fender and down a narrow aisle lined with batteries and spray cans, John Hosken snaps up a box of brake shoes. ''Ten years ago, nobody thought twice about what brake linings were made of, '' says the auto repair shop owner. Today, most mechanics know they contain asbestos - a substance believed to pose potentially serious health hazards. As a result, mechanics avoid blowing dust from the linings into the air.
Mr. Hosken says he'd now like to know more about the dozens of chemicals used in his shop - for everything from cleaning oily parts to drying wire cables.
His attitude reflects a growing national concern over hazardous substances used in US workplaces. The search for safer conditions has created momentum behind ''right-to-know'' laws.
These laws require businesses to tell employees the names of any hazardous substances used on the job and the potential health problems associated with them. Some also require the information be made available to local communities.
At least eight states, including Michigan, California, and New York, have some sort of right-to-know law. A growing number of cities and counties have forged laws as well.
Right-to-know advocates - which include community leaders, firefighters, union organizers, and workers - say they intend to continue pushing until all states are covered by some form of the legislation. Differing versions of the law have been introduced in over 20 states, plus several where existing legislation is being expanded or modified.
The laws affect a wide range of businesses, from large chemical manufacturers and automakers to restaurants and hotels where barrels of cleaning liquid are stored. Most of the laws specify that labels be put on containers and information sheets be kept, detailing hazards and proper handling procedures.
Organized labor began seeking a federal right-to-know regulation in the early 1970s. In the last two years, however, focus has shifted to state and local initiatives.
''Our clear preference is to have a strong federal regulation,'' says Richard Lewis of the International Chemical Workers Union. ''But in the absence of that, we'll continue to support state and local initiatives.''
Industry officials, meanwhile, argue that this mishmash of laws makes it costly and complicated to do business.
''If a company has plants in 25 states, it could someday be faced with that many different systems for identifying chemicals,'' says Charles Van Vlack, a spokesman for the Chemical Manufacturers Association. He says most companies already have methods for identifying hazardous substances, such as color coding or numbers.
In 1981, the Reagan administration withdrew a proposed regulation from the Occupational Safety and Health Administration which would have required labeling of certain chemicals. The administration then proposed its own OSHA regulation, called the Hazardous Communication Program. Among other things, it would allow companies to decide themselves which chemicals are hazardous.
Many companies favor this self-regulating approach and are eager to see the standard put into effect, since it may preempt the growing array of state and local laws.
But backers of right-to-know laws complain the regulation lacks the teeth of the earlier version. One labor union critic says it ''gives companies trade-secret loopholes you could drive a truck through.''
A point of conflict between industry and right-to-know advocates is the use of exact chemical names. Many businesses consider at least some of this information proprietary.
''There is the possibility of losing a competitive edge if you list every substance in a mixture,'' says Paul Wilkinson, a consultant on hazards communication for E. I. du Pont de Nemours & Co. Chemicalmakers estimate between 5 to 15 percent of the mixtures they sell would be classed as secret.
Says Mr. Wilkinson, ''We concentrate on telling people what the hazards are, rather than the chemical name.''
Right-to-know laws generally make allowances for holding back some trade secrets. But several proposed laws, such as those in New Jersey and Massachusetts, extend access to the community.
''Local citizens want to know what's being kept in the workplace, since it may end up in their air and water,'' says Peggy Seminario, an industrial hygenist with the AFL-CIO.
Firefighters and police say they especially need to know what hazardous substances are being stored. There have been cases when emergency workers had difficulties fighting fires or rescuing workers because they didn't know the nature of the chemicals present.
Many companies have worker education programs, designed to train employees in handling hazardous substances. At the same time, some workers tell of using powerful chemicals with few safety precautions.