Mr. Obama appears poised to sign the measure. An Environmental Protection Agency spokeswoman, Liz Purchia, called the final draft “a clear improvement over current law.”

Under the new bill, E.P.A. regulations would pre-empt most new state regulations, although states could still enact measures such as monitoring and labeling of chemicals. State chemical restrictions passed before April 22 would be allowed to stand. Environmental groups failed in their push to allow states to enact laws stronger than federal rules.

Daniel Rosenberg of the Natural Resources Defense Council said Thursday that the new bill was still too weak, citing its pre-emption of states’ authority, its failure to provide the E.P.A. with enough authority to check imported products, and its restrictions on citizens’ abilities to petition the E.P.A.

But the authors of the bill say it would strengthen the law in other ways. Under the 1976 law, the E.P.A. is required to evaluate the safety of new chemicals introduced in the marketplace but not the roughly 64,000 chemicals that were already being used in American commerce. Since then, about 22,000 new chemicals have been introduced and evaluated, and those the agency designates as toxic and hazardous are subject to regulation.

The new measure would require the E.P.A. to begin evaluating those untested chemicals. The E.P.A. would be required to prioritize high-risk chemicals and to test at least 20 chemicals at any given moment, with each test limited to seven years. User fees of as much as $25 million a year would be levied on companies to help pay for the testing.

Those mandates still fall far short of what environmental advocates had once envisioned, a law requiring the E.P.A. to test up to 300 existing chemicals a year.

The new legislation would also require the E.P.A. to take only the health and environmental effects of a chemical into account when devising new rules, not the financial effect of those regulations. The existing law requires new chemical regulations to consider compliance costs.