IN TODAY’S Washington, it’s strange enough to see a burst of bipartisanship. Odder still is that the unexpected cooperation might lead to the first major environmental law enacted since the 1990s.

The Toxic Substances Control Act, which was supposed to give the Environmental Protection Agency (EPA) the authority to regulate potentially dangerous chemicals, has been on the books since 1976. Yet it is such a shambles that, in all that time, the agency has used it to ban only five chemicals. The law allowed thousands of chemicals to stay on the market with no review, and it made the process of vetting new ones so difficult that they have been barely regulated at all. The EPA can’t even demand testing without undergoing a grueling rule-making process and demonstrating that a chemical is risky. The agency — somehow — has to provide data to get data. And even with alarming information on a particular chemical, the EPA must clear a very high legal bar to ban or limit its use. In 1991 a court threw out the EPA’s ban on asbestos, a notorious carcinogen.

For years, Sen. Frank Lautenberg (D-N.J.) has tried in vain to improve the law. Then last week he and Sen. David Vitter (R-La.) announced a bipartisan compromise. Under the Lautenberg-Vitter bill, the EPA would have the authority to review chemicals in current use, with more power to demand testing when it suspects a substance to be dangerous. Before new chemicals could come to market, the agency would have to decide that they are likely to be reasonably safe.

With help from centrist Sen. Joe Manchin III (D-W.Va.), the legislation has attracted 10 co-sponsors from each party, including conservatives such as Sens. James M. Inhofe (R-Okla.) and Marco Rubio (R-Fla.), along with a good chunk of the Democratic Senate leadership.

Some environmentalists, though, are unhappy. They look at what Mr. Lautenberg proposed in years past and despair that the bipartisan version is too diluted. Reform, they say, should establish a far stronger review standard: The EPA must have a reasonable certainty that a chemical will do no harm. The critics worry that the new law would quash state-level efforts. And they point out that the current bill lacks firm deadlines — for example, on the EPA finishing its review of chemicals already on the market. Industry support for the legislation only heightens their concerns.

In fact, the bill’s review standard would have the effect of focusing EPA resources on higher-risk substances. Its authors were right to balance a legitimate interest in maintaining an innovative and profitable chemicals industry against public health demands. There is also value — economic and regulatory — in having a standard across the country, rather than a state-by-state patchwork that fails to protect millions of Americans. And, by the way, this package has a chance of becoming law.

The legislation could use tighter language on deadlines and in some other provisions, and it mustn’t end up precluding all state-level action. Senators will have option of tinkering with it on the floor. But they shouldn’t let this unexpected opportunity go by.