THE OCCUPATIONAL Safety and Health Administration has cut the amount of benzene to which a worker can legally be exposed by 90 percent. That is long-overdue good news; the old exposure standard was too high, and people were dying from it. But the benzene standard now issued at last is a classic example of what is wrong with OSHA. The occasion calls less for a celebration than for a wake.

OSHA has never had the resources to combat all the dangers facing workers. There has always been debate about the agency's agenda: Which are the greatest dangers, which should it tackle first? But benzene made almost everyone's hit list. The petroleum distillate is ubiquitous and a known carcinogen. It turns up in the energy, chemical, printing, plastics, rubber, steel, paint and countless other industries; it is widely used as a solvent. The government estimates that a quarter million workers are regularly exposed. There used to be more; the number declined as the dangers became better known. The dosages are in dispute, but among other things it is clear that steady exposure to benzene greatly increases the chances of leukemia.

Even so it took more than 10 years to promulgate the new standard, which OSHA first issued in 1977. The earlier version was taken to court by the American Petroleum Institute and others on grounds that the agency had neither documented that benzene was a significant risk nor shown that the proposed new standard would substantially reduce that risk; it had to be redone. It is hardly unreasonable to insist that a regulation that will cost millions of dollars to carry out be based on good science. But the science of these risks can never be exact, and the rule of thumb may be that the greater the risk from a substance -- the more entrenched it is in the economy and the greater the number of workers exposed -- the greater will be the resistance to its regulation.

OSHA has tended over the years to proceed against dangerous substances one by one. Benzene, which should have been easy, teaches that that won't work. The process is too slow, the field too vast. Here as in certain other areas -- pesticides come to mind -- Congress may have to confer a broader authority, or the job will never get done. Perhaps the agencies should be allowed in some circumstances to move against entire groups of chemicals. Do they have all the power they should to do so now? It may also be that OSHA does the most good not when it regulates particular chemicals, but when it sets out broader industrial practices, as, for example, when it recently required that workers be forearmed by being told when they are working near dangerous substances.

But it's time to rethink what OSHA does, the strategy to follow. The benzene standard is nice to have, but the broader record of accomplishment is paltry.