A LEGAL LOOPHOLE is complicating efforts by drug-enforcement officials to staunch the flow of marijuana and cocaine from Latin America into the southeastern United States. That region has become the major channel of the drug traffic since enforcement efforts focused on California and the Southwest began to take hold. Most of the drugs reaching the area are being transported by seagoing cargo ships to locations outside the 12-mile limit of U.S. territorial waters. There they load their illicit cargo aboard small, fast "courier" boats for transport ashore. Federal officials can and do intecept these boats as they head toward shore. But, obviously, it would be more effective to confiscate the drugs before they leave the mother ship and to arrest the crews.

That effort, however, has been hampered not only by the need for international cooperation in combating drug smuggling, but by a serious omission in U.S. drug laws. Because of the omission, it is no crime now for a U.S. citizen or a U.S. - registered ship outside territorial waters to have illegal drugs aboard. Civil statuates allow the drugs and the ship to be confiscated. But there can be no criminal prosecution of the people (whether American or foreign nationals) involved unless intent to smuggled the drugs into the United States can be proved. The huge amounts of money invovled in even a single large drug transaction reduce the practical effects of the loss of one cargo ship to almost nothing. Thus, the deterrent effect - prosecution of the drug runners - is lacking.

Drug officials are urgiing a revision of federal statutes and international treaties to amend that oversight. In our view, that's a good idea. They've also begun applying a federal law, originally enacted during Prohibition, that allows the Coast Guard to board any vessel outside territorial waters if it can prove that U.S. - registered boats have tried to smuggle some of the ship's cargo ashore. A White House task force also is studying other ways - including closer cooperation with other countries and the use of military radar planes to track suspicious cargo ships on the high seas - of combatting seaborne drug smuggling. These are welcome actions. They show that drug officials have learned well a lesson of the past decade: The pervasive, corrupting effects of the drug trade make it imperative to respond quickly whenever it makes a new appearance.