WASHINGTON—Amid shrieks from critics, the Bush administration announced that it has loosened industrial air pollution rules.

The administration said the changes would encourage plant improvements that would clean the air. "The need for reform is clear and has broad-based support," says Christie Whitman, Environmental Protection Agency administrator. "The current rules have deterred companies from implementing projects that would increase energy efficiency and decrease air pollution." But critics denounce the changes. They say the current, tougher rules require factories to make investments in pollution control equipment when they modernize.

The dilemma of the existing rules, experts say, is that new technologies are available that would make plants marginally cleaner or more productive. But installing those improvements would require that the owner bring the plant up to modern pollution standards. Thus, small improvements are discouraged.

The new rules apply to industrial plants, including manufacturing plants and oil refineries. Proposals for additional rules that would apply primarily to power plants will be issued shortly.

The changes, which took effect in November, allow plants that install state-of-the-art pollution control equipment to operate for 10 years before being forced to review new technologies. Opponents say this lets plants ignore pollution technology improvements that come in the 10-year period.

Industrial plants with many smokestacks or other sources of air pollution will also be able to clean up one emissions source on the premises while allowing others to get dirtier, as long as the total emissions decline. This rule is intended to benefit pharmaceutical manufacturers, semiconductor factories, automobile plants and other quick-to-market industries.

Perhaps more disturbing to state environmental officials is a rule that lets plants undertake more extensive changes without triggering requirements to reduce their emissions. Under previous rules, certain physical changes to plants required their owners to install pollution control equipment. But under the new rule, plants could make whatever changes they wanted without scrutiny, as long as the cost of the changes were below a certain level.