Something good is happening to our national security debate. Hawks and doves are finding common ground. A sensible and sustainable consensus may be heaving into view.

Now, it is ancient history, dating back at least to that December day when the Red Army plunged into Afghanistan, that doves are moving right. Jimmy Carter's reversal has been confessed and chronicled. Even George Kennan has found it prudent to hedge that "no one can guarantee, of course," that the Soviet invasion was not a prellude to military aggression farther afield. Only the scope, not the fact, of the Soviet Union's readiness to take local advantage of its newly and expensively acquired global military reach is now in contention.

What is new is the flow in the opposite direction. Conservatives, known for their alarms, are coming up with analyses made in the past by liberals with a restrained attitude toward Soviet power.

The first sign of this popped up in a recent Foreign Affairs article by Rober W. Tucker of Johns Hopkins University, who achieved a certain note after 1973 by making the case for a war for oil. He described the invasion of Afghanistan as a signal that we have entered "a very dangerous period" in which "a great military power has emerged intent on altering the global status quoe" -- good traditional conservative fare.

What was head-turning was to see Tucker go on to suggest that the Soviet Union's lower material base might make its military edge temporary, if the United States and its allies set about redressing the military balance. Informed liberals have been underlining for some years that the Soviet economy is in an unmistakable slow- or no-growth crisis and that this puts inescapable restraints on defense.

To find a rigorous thinker like Tucker making the same point did not exactly take the chill off his warning that Soviet risk-takers may be tempted to exploit the period until the United States can catch up. But it did seem to restore a useful perspective. It is one thing for the United States to contemplate going to war to serve its strategic aims. It is another to serve those aims by increasing defense spending a few percentage points -- off a GNP nearly three times Moscow's.

Now comes another tone-setting hawk, Gerogetown's Edward N. Luttwak, writing in the new Commentary.He warns that the Kremlin, emboldened especially by its new and newly earned (in Afghanitsan and Ethiopia) operational confidence in its armed forces, is being drawn to seek "a permanent enhancement of its position in some decisive map-changing way. "No surprise there.

But he, too, contends that "the time period in which the 'window' of Soviet military advantage is projected to close happens to coincide with the advent in full force of a restriction on the Soviet economy whose first signs are already with us." For instance, "mostly Muslim and backward" Central Asians are flooding the Soviet labor force.

But this is not all. In a paragraph of a lucidity and balance that would have set hawks to screaming if George Kennan had drafted it, Luttwak explains how the West was saved:

". . . by coincidence, the gradual recovery of American realism about the outside world after 1975, the death of Mao and the fall of the Gang of Four in 1976, and the first stirrings of belated alarm in Western Europe have all created circumstances in which the decline in the military effort . . . has been reversed, so that a modest but accelerating recovery is now under way. Even at a net annual growth that is in reality well short of the much-publicized 3 percent U.S.-NATO budget target, the trend has now become adverse for the Soviet Union. . . . Thus, instead of being free to expect an open-ended period of growing military advantage, the Soveit Union is now confronted with a transitory period of superiority that will end -- on present trends -- in the later 1980s. . . ."

All of us could embroider what Tucker and Luttwak have to say. But let us get to the main point. Conservatives have rightly asked for a recognition that Soviet power poses a problem that cannot be dealt with on a business-as-usual basis. Liberals have rightly asked that the American response be based on more than selective worst-case alarms. Are the two camps finally listening to each other? Is the debate coming to an end?