Roberto D'Aubuisson, the right-wing leader who consolidated his position in the recent elections in El Salvador, is running an early test of the Reagan administration's taste for his rule. He has formally blocked or suspended major parts of the land reform that was at least the rhetorical centerpiece of the program of the junta in power before the elections. He is sending word to Washington that its emphasis on reform is blocking El Salvador's reach for democracy, free enterprise and victory in the battlefield.

Mr. D'Aubuisson's argument is not without superficial appeal. Land reform is a painful and difficult exercise in the best of times, and El Salvador is living through the worst of times. The pre-election junta had already gone into low gear on the reform, although, out of deference to the program's high political profile in Washington, it had done so discreetly. The program was drawn up mainly by Americans in a hurry and, in other circumstances, there might well be reason and support for a more measured pace and a certain retooling.

But this is not what is going on. Before the elections, the social elements represented by the parties of the right fought reform with terror and delay. Now that they dominate the legislature, they are seizing on the program's flaws to roll back the formal commitment to reform and to discredit its Salvadoran partisans. No objective observer can avoid the suspicion that the Salvadoran right means not simply to correct flaws but also to restore the old order under the banner of its ostensible electoral mandate.

If the Salvadorans really wish to turn back the clock, the United States cannot and should not stop them. But that does not seem to us what the voters were asking for--the pro-reform Christian Democrats, after all, were the top party. In any event, it is not conceivably a turn that the United States would want to endorse and to pay for.

Sen. Percy, chairman of the Foreign Relations Committee, vows that "not one cent" of American aid will flow if land redistribution is suspended. There is a need to ensure that the particular programs on which Americans insist are programs that forward-looking Salvadorans approve. But Sen. Percy's is a sentiment that commands broad backing in Congress. The administration should present it to the parties in El Salvador as a concrete political reality with which they must deal. Otherwise, Mr. D'Aubuisson may conclude that, so far as this administration is concerned, anything goes.