WASHINGTON — A divided federal appeals court Tuesday overturned a regulation clamping down on power plant pollution that contributes to unhealthy air in neighboring states.

In a 2-1 decision, a panel of the U.S. Court of Appeals for the District of Columbia Circuit said the Environmental Protection Agency’s cross-state air pollution rule exceeded the agency’s statutory authority. The court faulted the EPA for imposing “massive emissions reduction requirements” on upwind states without regard to limits imposed by law.

In adopting the regulation a year ago, the EPA sought to reduce downwind pollution from power plants in more than two-dozen states. The rule was scheduled to go into effect in January, but several large power companies and some states sued to stop it. The appeals court agreed last December to suspend the rule pending its review.