Under a proposal from the U.S. Environmental Protection Agency, industrial companies would be freed from reporting most chemical releases of less than 5,000 pounds, up from 500 pounds under current law. Factories, power plants, refineries and other sources of pollution also would need to report their releases only every other year instead of annually.

A top agency official said the changes would reduce the regulatory burden on industries while giving the EPA more time to review the data for trends, such as whether releases of a specific chemical are on the rise or if a certain industry or factory is having problems.

"We spend so much time receiving forms and entering the data that we don't have enough time to analyze it," Kimberly Nelson, the EPA's assistant administrator for environmental information, said in an interview.

Critics of the plan say it would weaken a 1986 law that by all accounts has nudged companies to curb pollution by giving the public more information about chemical releases. Congress created the Toxics Release Inventory in response to a chemical catastrophe at a Union Carbide plant in Bhopal, India, that killed more than 2,000 people.

The critics note that people and groups already perform their own analyses of the EPA's data. Cutting the amount of information provided and releasing it less frequently would make it more difficult to track some companies and determine pollution trends, they said.

"Now it's companies first and communities last," said Sean Moulton, a policy analyst with OMB Watch, a Washington-based advocacy group. "I can't really believe they want to do this."

The EPA's own Web site touts the chemical inventory's benefits, boasting that "communities have more power to hold companies accountable and make informed decisions about how toxic chemicals are managed." The agency puts the data on its Web site, and with a few clicks of a computer mouse, anyone can find information about specific industries and plants or about 650 different chemicals. The data can be ranked nationwide or by state, county, city and ZIP code.

When residents in Chicago's Pilsen neighborhood wanted to know if metallic-tasting smoke churning through the streets was dangerous, they turned to the EPA's database for answers.

What they found while scrolling through the list of polluters alarmed them: The H. Kramer and Co. smelter at 21st and Throop Streets is the largest source of airborne lead in the Chicago area.

Organized into a small but tenacious group, the plant's neighbors started badgering elected officials and environmental regulators, prompting a state investigation that found high levels of lead in several backyards.

While H. Kramer denies it is responsible for lead in the neighborhood, the company has agreed to clean up its property and reduce its emissions.

"What the EPA is talking about is really disturbing," said Karen Sheets, spokeswoman for the Pilsen Environmental Rights and Reform Organization.

In Colorado, researchers used the database to reveal that chemical releases are more concentrated in the Rocky Mountain states than in the country as a whole.

A Brush Wellman alloy factory outside Toledo, Ohio, cut emissions of beryllium, a toxic metal, after environmental groups used the EPA inventory to highlight the company's releases. A similar campaign led a Rohm and Haas chemical plant near Cincinnati to reduce airborne chloromethane, which the EPA considers a possible carcinogen.

The annual reports of chemical releases are two years old by the time the information is made public. Critics of the proposed changes say moving the reports to once every other year would make it more difficult to pressure industries to keep reducing emissions.

The vast majority of chemical releases still would be made public, Nelson said. For instance, the proposal would affect only 3 percent of the nationwide emissions of trichloroethylene, a cancer-causing chemical known as TCE.

For some chemicals, though, the number of companies required to report releases would drop significantly, meaning information about some polluters would not be available to nearby communities. Nearly half of the companies that reported TCE emissions during 2003 no longer would be required to do so, according to a Tribune review of the database.

"I thought the idea was to give people more information, not less, about factories in their cities and neighborhoods," said Sandy Buchanan, executive director of Ohio Citizen Action.

Under the 1986 law that created the chemical inventory, the EPA must inform Congress of proposed changes at least a year in advance. The rules would take effect unless challenged by lawmakers or the public.

Business groups are lining up behind the change. "This sensible update will provide relief to small manufacturers and free up resources for addressing critical environmental priorities," John Engler, president of the National Association of Manufacturers, said in a statement.