THE FEDERAL Nuclear Regulatory Commission has broken the stalemate over two big reactors, Shoreham on Long Island and Seabrook in New Hampshire, that are now completed. The governors of New York and Massachusetts, Mario Cuomo and Michael Dukakis, have respectively been blocking their operating licenses by refusing to cooperate in emergency planning to deal with accidents. The Seabrook planning area spills over into Mr. Dukakis' state, giving him, under the previous practice, leverage to prevent licensing simply by declining to work with New Hampshire's Gov. John Sununu.

When the state and local governments won't take part, the NRC's new rules enable its licensing board to consider plans drawn up by the utility that operates the plant. That's clearly second-best, as the NRC acknowledges, but it's better than allowing a governor to hold up indefinitely a plant that, over a decade of planning and construction, has won all the successive required approvals and met every standard.

There's no doubt that the NRC is reflecting congressional intent. In an attempt to exempt these two reactors from the new policy, a Massachusetts congressman, Edward J. Markey, brought legislation to the House floor last August. It was defeated, 261 to 160. Licensing reactors, and setting safety standards, are properly the federal government's job.

The American Northeast, meaning New York State and New England, doesn't like any of the major sources of electric power. It doesn't like coal because of air pollution, and the Northeast remains much more dependent than the rest of the country on oil and nuclear power. Events in the Persian Gulf certainly don't encourage greater dependence on imported fuel oil now. That leaves nuclear power -- but the governors of Massachusetts and New York don't care for that one either.

The Northeast's solution is to import large and increasing amounts of its power from Canada. Most of it is hydroelectric; some is nuclear. The Northeast is managing to avoid hard choices by relying on generating plants built by others, beyond its own borders. That's a pretty clear demonstration of the reason for keeping final decisions in the hands of the federal government, where the responsibility for the national energy supply rests.