The Kremlin is right to accuse President Carter of having "ignored the fact that aggression had been committed" against Ethiopia by Somalia. The facts of Somalia's agression are indisputable, and the President did ignore them in his press-conference statement.

True, the United States is not supplying arms to Somalia as the Soviet Union is supplying them to Ethiopia. True, Carter is urging Somalia and Ethiopia to stop fighting and to start negotiating. The Kremlin, on the other hands, greatly increased its arms shipments to Ethiopia once it saw that the United States was taking no action to counter Moscow's initially small involment.

The Kremlin is no better than the White House - indeed, it is much worse. Carter's sin is one of omission, in failing to speak out clearly against a case of aggression, but the Kremlin's is a sin of commission, in that it provoked the agression. For it is Moscow's pursuit of its new imperial ambition in Africa, and in the first place in Somalia when the two were still as thick as thieves, that started the trouble.

But even here the Carter administration cannot be absolved of all blame. Carter at first encouraged Somalia to believe that, if it got rid of the Russians, the United States stood ready to take their place and to provide the arms and other aid previously provided by Moscow. Had it not been for such hints from Washington, which were withdrawn when wiser counsels prevailed, Somalia might never have moved against Ethiopia. But while Washington is wrong to act now as if Somalia were not the agressor, it is the Soviet Union that brought about the agression in the first place.

If the Kremlin had not for years been pumping arms into Somalia, which it was building into a major naval base and political outpost in Africa, the Somalis would have had neither the weapons nor the inclination to attack Ethiopia. It was Soviet military equipment and training, to the tune of $1 billion, to say nothing of the particularly virulent brand of Marxism that Moscow fosters in its African clients, that welded a nomad nation of 3 million into a fighting force eager to invade a much bigger neighbor.

Some such purpose figured in Moscow's original plans long before Angola provided it with an opportunity to send Cubans to Africa. When the Soviet Union first moved into Somalia, the Kremlin regarded it as a stepping stone to Ethiopia, which was then America's foremost client and outpost in that part of the world, with its forces equipped and trained by the United States. But when a radical Marxist military clique took power in Ethiopia, the Kremlin's greed made it urge the Ethiopian military to throw out the Americans so that Soviet influnce could move into the vacuum. Once Moscow started pumping arms into Ethiopia - which now equal in value the $1 billion it had previously supplied to Somalia - the fat was in the fire.

Angola was the first move the Soviet Union made as part of its new design for Africa. Ethiopia is the second. What will be the third? We don't know, but we can be sure that unless the Soviet Union is stopped dead in its tracks, there will be a third, and then a fourth, and many more after that.

As in Angola, the Cubans are acting on the Kremlin's behalf, but again we hear the argument that they are really there on their own account. In the case of Angola, some Washington officials used intelligence information to show that Cuba was the main actor, and that Moscow was only dragged in by Castro. Those who urged this view at least have the excuse that they were taken in by deliberately planted false information. There is no such excuse now. Both the Cubans and the Russians are there to show that the Soviet Union has the power to help a client state mount a successful military offensive - and the lesson will not be lost on Africa, or on the rest of the world.

The question now is whether the Ethiopian army with Cuban participants and Soviet advisers will stop when it reaches the Somali border, or will drive on to the sea, to regain for the Kremln the Somall coast and the Soviet Union's only naval base in teh Indian Ocean. Moscow regarded the base as one of its key strategic assets, and it can be excepted to do everything possible to get it back into its Ethiopian adventure as a test of its new policy of expansion, and of the Carter administration's reaction to that policy.

During the election campaign, candidate Jimmy Carter sought to make political capital out of the Ford administration's mishandling of Angola, and he left the distinct impression that a Carter administration would not allow a similar situation to occur. The Soviet move into Ethiopia can be seen, however, as an even more dangerous action than the move into Angola. The time has come for the Carter administration to act - and this does not mean that the United States should become directly or indirectly involved in the fighting. To do so would be to behave no better than the Russians have behaved.

Nor can Washington tell Moscow that Soviet actions in Ethiopia threaten the strategic arms limitation talks. Indeed, in the administration's view SALT is so central to the security of both countries that to link it with what happens in Ethiopia would not make diplomatic or strategic sense. Moscow knows this, and would not respond to pressure on that front. But Ethiopia is the Carter administration's Angola.

If Carter fails to stop the Russians, he will be storing up trouble for himself - and he will be helping the more expansionist faction in the Kremlin. The Moscow hawks certainly argued that U.S. inaction over Angola made it safe to act in Ethiopia - and they will now argue that Carter's inaction over Ethiopia would make it safe to reach for an even bigger prize the next time. U.S. policy planners know all this, and they are now trying to fashion the tools that will stop the Russians.