HAS JIMMY CARTER finally gotten through to the Europeans on the hostage crisis? It reflects welcome if overdue progress that the question can now be asked at all. A fortnight ago, it was all too plain that most of the allies were looking the other way. Yesterday in Luxembourg, however, the foreign ministers of the European Economic Community gave another answer. It was not entirely straightforward: the nine ministers agreed to take certain lesser steps now and to adopt tough economic measures at their next meeting on May 17 -- measures that could be painful for Europe and for Iran -- if there is no break in the crisis. But not withstinding the pulling and hauling between the British and Germans on the one hand and the French on the other, it was an alliance answer, and its general direction and tone were true.

One reason for the shift seems to be that the Europeans have at last heard the American insistence that the hostage issue is unlike those other issues on which different viewpoint are normally expressed on opposite sides of the Atlantic. The hostage issue, Americans have been saying, is special.

But the key element in the shift was clearly Mr. Carter's recent decision to make an explicit threat of military action if sanctions do not work. American military action would have a great impact on the allies. They could avoid taking Mr. Carter's threat seriously only at their peril. Even while making the threat, however, Mr. Carter offered the allies an important chance to influence American policy. He conditioned the American response not just on the application and failure of American sanctions but on the application and failure of sanctions by the allies, too.

By this formulation he was not only putting pressure on the allies to help. He was also assuring them that the United States would not undertake military action without giving them the opportunity to make that action unnecessary. This is the opportunity to which the allies responded at Luxembourg. They could not have done less and still insisted to their publics that they were doing everything they could to support Washington, to give Iran incentive and adequate time to respond in moderation, and to reduce the prospects for the use of force.

The Europeans, all together, are now publicly committed to a course leading to the imposition of major sanctions in less than a month and to the countenancing of military action after that. The sanctions are the substantial ones for which they voted, knowing that a Soviet veto would spare them the consequences, in the Security Council last January 10. The allies will be able (and obligated) to show their seriousness in the weeks leading up to May 17 by enacting the enabling legislation that is the appropriate basis for sanctions in the absence of a council resolution. The allies are, it is now possible to say, finally acting like allies.