In one of its most far-reaching environmental actions, the Bush administration signed a rule that will allow thousands of power plants, refineries, pulp and paper mills, chemical plants and other industrial facilities to make extensive upgrades that increase pollutants without having to install new antipollution devices.

Jeffrey Holmstead, the E.P.A. administrator for air programs, said today, "We wish we had better data, but we're confident this rule will not have an emissions impact."

The rule allows industrial plants to avoid installing pollution-control devices when they replace equipment, even if the upgrade increases pollution, as long as the cost of the replacement is less than 20 percent of the cost of essential production equipment.