The ability of strongman Manuel Noriega to stay in power in Panama despite a national strike is, frankly, frustrating.

So frustrating that Washington is casting about for ways to exert more pressure to get Noriega widely suspected of drug smuggling, bribe taking, and political murder to go.It isn't easy to find effective methods of exerting such pressure. Though Washington is considering trade sanctions even tougher than those it imposed the other day, they seldom prove effective. As for the U.S. invasion that Noriega fears, it would be a big blunder. There is no clear danger to U.S. citizens and interests that would justify military action. Moreover, an invasion of Panama would be bitterly resented throughout Latin America.

There is, however, another card the U.S. should consider playing. It involves the treaty by which the U.S. is scheduled to yield control of the Panama Canal to the Panamanian government on Dec. 31, 1999.

If the U.S. started talking about backing off from that agreement, it just might generate enough internal pressure to topple Noriega. And there's ample justification for the U.S. to at least reconsider the pact.

Even before the current crisis, the U.S. was complaining to Panama about neglect and mismanagement involving the canal. Inexperienced Panamanian military officers are said to have been put in charge of some agencies dealing with the canal. Moreover, canal-related Panamanian jobs have been politicized.

More recently, the discredited Noriega regime has been violating the treaty on at least two counts. Last month, contrary to the treaty, it started imposing a "lights and buoy fee" on ships using the canal. Panama also has tried to override a treaty clause allowing ships through the canal on a first-come, first-served basis.

If the U.S. doesn't get tough on such treaty violations, it can expect more serious ones. There's no reason to tolerate a one-sided arrangement, particularly since the Panama Canal is still vital to America's national interest.

Cargo shipped through the canal comprises a modest share of the total seaborne commercial tonnage into and out of the United States. But for certain commodities grain shipped to Asia, and Japanese autos shipped to the East Coast, for instance the canal is still the route of choice.

Moreover, despite changing military technology, the canal still plays a key role in U.S. defense planning. The canal remains extremely important because it cuts more than 6,000 miles and two to three weeks from a voyage between the Atlantic and Pacific oceans.

The U.S. has a right to get as tough as it takes to make sure the safeguards in the Panama Canal treaty are not ignored by an unelected thug like Noriega or anyone else, for that matter.