How often does Congress think it can keep tinkering with the laws governing the Central Intelligence Agency without turning them into meaningless mush and rendering the agency impotent?

Or is that the objective of these repeated efforts at fine-tuning?A few days ago, a new chapter in this continuing saga was written when the House and Senate agreed on legislation aimed at preventing a repeat performance of the kinds of unauthorized covert operations by the CIA and other intelligence agencies that marked the Iran-Contra scandal.

The kindest thing that can be said about this legislation is that it reflects growing congressional optimism to the effect that covert operations are no longer as necessary as they once were now that the Soviet Union has pulled in its horns somewhat and the Cold War is supposedly over.

The most realistic thing that can be said about it is that the legislation represents an attempt to keep Congress more informed about what the CIA and other U.S. intelligence agencies are doing.

The trouble is that the more Congress knows about secret intelligence operations, the more some lawmakers tend to talk publicly about them, impairing the CIA's effectiveness and endangering the lives of American agents.

Likewise, the more Congress knows about such operations, the more the legislative branch of government is tempted to try to micro-manage agencies that are supposed to be run by the executive branch.

Under one change, the new legislation defines a covert operation as a secret activity "in support of national foreign policy objectives abroad." Previously, it was defined as a mission "important to the national security of the United States." Some difference.

Another new provision permits the use of third countries to fund covert operations. But this already was being done, and a new law was not needed to authorize the practice.

More constructively, the new measure requires the president to put in writing his decision to begin a covert operation and submit the document to congressional intelligence committees in advance of the operation, rather than informing them orally after an operation starts.

Fine. But the new measure amounts to a tacit admission that Congress didn't do a good enough job when it tightened intelligence agency laws after the Nixon years. The prospect of still more tinkering is raised by the fact that the new measure contains no criminal penalties for violations of its provisions.

The most serious problem, though, is that Congress keeps tightening requirements on the executive branch without tightening its own end of intelligence activities. By their very nature, those activities must largely be kept secret. But the more people who look over the shoulders of the CIA, the harder it is to keep legitimate secrets. And the agency is supervised not just by one or two but several congressional oversight committees. Both the number and size of those committees should be reduced.

As it is now, the CIA often has trouble winning cooperation from some other countries because even our allies have concluded that excess congressional intervention has made American intelligence operations too prone to leaks.

The next time Congress tinkers with the CIA - and there undoubtedly will be a next time - the lawmakers should aim the reforms at their own part of intelligence programs.