WASHINGTON — The Supreme Court let stand Monday a lower court ruling that paved the way for Congress to vote on the North American Free Trade Agreement without having an environmental impact study in hand.

Last June, a legal challenge to NAFTA by Ralph Nader’s Public Citizen group and the Sierra Club threatened the pact’s future when a federal judge ordered the costly and time-consuming study be done. In September, the U.S. Circuit Court of Appeals for the District of Columbia reversed the decision.

Although Congress subsequently approved NAFTA in November, the two advocacy groups argued to the Supreme Court that review of the decision was “part of a larger controversy” centering on whether such studies are required for all trade agreements.

The groups specifically referred to the upcoming congressional vote on GATT. President Clinton is expected to send the global pact to Capitol Hill sometime after April 15.

The High Court rejected without comment the request to hear the appeal.