STILL ANOTHER rider that would vitiate environmental law has become an issue as this hapless Congress struggles to complete its year's work and go home. This one was added to the defense appropriations bill, which Congress cleared and the president signed last month.

It would exempt defense agencies from payment of fines or penalties for any "environmental violation" by any military installation or facility unless the payment was "specifically authorized" by Congress. It is said to have been inserted by Senate Appropriations Committee Chairman Ted Stevens in response to an effort to enforce the Clean Air Act against a military installation in Alaska.

The rider is terrible policy. The national association of state attorneys general, who play a leading role in enforcing many federal environmental laws, reminded the congressional leadership in a letter a few weeks ago that "The federal government is, and has long been, the nation's largest polluter." Military installations are a major contributor. They ought not be exempt; nor should the legislative branch seek to make itself the arbiter of a system of selective law enforcement.

The president said in signing the appropriations bill that he was ordering defense officials to seek prompt authorization from Congress to pay fines they incurred. That's not good enough. Efforts are underway in both houses, the Senate particularly, to add what would amount to a reverse rider to the omni-appropriations bill with which the session will conclude, rescinding the Stevens language. Some members seek a compromise in which it would be rescinded only in part. That's not good enough either. In other contexts, this Congress prides itself on being tough with regard to law enforcement. Why only some laws, and not these? They can fix this if they will -- and they should.