(CBS/AP) In a victory for industrial plant operators, the Environmental Protection Agency is preparing to issue a new rule within days to let thousands more facilities modernize without adding more pollution controls.

The New York Times first reported the story Friday, and it was confirmed Saturday by EPA officials.

Under the new rules, an old factory will be able to make additions equal to the cost of replacing 20 percent of its equipment without having to add pollution controls, the Times reported.

At issue is a process called New Source Review.

The Clean Air act requires pollution controls whenever a factory was built or upgraded. But existing factories can escape the law under certain circumstances.

If the upgrade were deemed "routine maintenance," the factory would be exempt. But if the upgrade constituted something more than routine upkeep, it was subject to the Clean Air rules — meaning companies had to install costly pollution controls.

Industry said the requirement was vague and discouraged plants from switching to newer, safer, more efficient equipment — machines that might actually emit less pollution.

According to The Times, the Bush administration has considered changing it since President Bush took office.

The new rule relaxes the agency's definition of "routine maintenance," a catch-phrase Congress adopted in its 1977 Clean Air Act amendments to describe the only reason an industry could modernize without having to install best-of-breed pollution control technology.

"Routine maintenance" has been at the center of debate over the new source review program, which was intended to force businesses to install new clean-air devices if they modified or improved older plants in ways that increase emissions.

Bush administration members and industry officials who lobbied heavily for the changes describe them as clarifications of a confusing standard that has long stymied industry. The new source review program needs improving, said the EPA's acting administrator, Marianne L. Horinko, because "that program is not causing a whole lot of emissions reductions."

Horinko said she will sign the new rule, which is based on EPA's proposal last November, in the coming week and it will take effect in the fall. The announcement is planned for Wednesday.

"This rule is desperately needed to make America's power plants, factories and refineries safe and reliable," said Jeffrey Marks, director of air quality policy for the National Association of Manufacturers.

Scott Segal, a lobbyist and attorney for six large utilities, said even the new allowance for replacement costs wouldn't fix all the shortcomings in the new source review program, but it would "move us along the path of improving efficiency and reliability of the electric power system."

Environmentalists, Democrats and other critics contend the rule change is a giveaway to utilities and industry, allowing many of the nation's dirtiest coal-burning power plants and other facilities to release millions of tons of additional pollution into the air.

"This latest rule on NSR is just one more flagrant violation of the Clean Air Act and every court's opinion on this matter," said Sen. James Jeffords, I-Vt., the No. 2 senator on the Senate Environment and Public Works Committee.

"This is the single most destructive anti-clean air rule in the history of the Clean Air Act," said Vickie Patton, a senior attorney in Boulder, Colo., for New York-based Environmental Defense, an advocacy group.

Some critics also have suggested the EPA announcement on the new rule was being moved up so that it would be out of the way if a Senate confirmation hearing begins next month for Utah Gov. Mike Leavitt, President Bush's nominee to succeed former EPA Administrator Christie Whitman. Horinko flatly denied that, saying "this was moving back when Whitman was here."

Horinko and other Bush administration officials have been largely silent on details of the new rule, fueling broad speculation about how much of a plant's modernization might be considered exempt.

Administration officials said only that the percentage - which one environmental group put at 20 percent based on a leaked draft of the new rule - was still subject to change.

"The concern about air emissions is way off-base," said James Connaughton, chairman of the White House Council on Environmental Quality. Still, he said the routine maintenance exemption "will be 50 percent or less, because that's what we proposed."

The EPA issued other changes to the new source review program last December that eased pollution-control requirements for utilities, oil companies and manufacturers. But the administration said last month it would briefly reconsider parts of those new rules, after several environmental groups and states downwind from the biggest industrial sources of air pollution sued to overturn them because of concern for public health.

Those parts include the length of time permitted between pollution-control upgrades, record-keeping and pollution reporting, and the way emissions are calculated.