THE REAGAN administration has maneuvered itself into an interesting contradiction over dealing with the Soviet Union. On the one hand, the president says the Communists are out to take over the world and an agreement made with them is not worth the paper it's written on. On the other hand, the secretary of state says that the Soviets must agree to a code of international conduct before the United States will negotiate with them, but if they do agree, the United States will negotiate.

So, you may ask, what's new in this? When has the United States not wanted to draw the Soviet Union into accepting some rules of the international game -- linkage? When has the United States not feared that, even if the rules could be drawn, they would not mean much? When has the Untied States not felt that, even if rules cannot be drawn, there may still be some advantage in making agreements? When has the United States not hoped to use the prospect of agreements as bait to induce the Soviets to accept rules?When has the United States not wondered if agreements were of real value?

These are the familiar sighs of the postwar era. They define the ambiguities that lie, unavoidably, at the heart of Soviet-American relations. No way has been found to get along with the Soviet Union, and no way without.

In fact, the Reagan administration is approaching this dilemma in its own style. It is not accepting it as a given, as something to be worked with and around. It is speaking, at least in this early period, as though fundamental changes in the nature of the relationship can be made. What officials evidently have in mind is to muster American power in all its aspects to impress upon the Kremlin that it must act with greater restraint. What aspects? One is to demonstrate at a capacity to buy and build more weapons. Another is to show that the United States can use force when and where it wants. A third is to support local elements resisting Soviet and Soviet-supported power. A fourth is to show that the United States can get along without agreements, and without rules, too.

Aside from its own self-confidence, which is considerable, this administration appears to have two rationales for its hard, hard-nosed, hard-to-get approach. It believes that it is tougher, more skillful, more committed and armed with a stronger political mandate than previous administrations to carry this off. It also believes that the Soviet union has chronic systemic weaknesses, in its economy, ethnic makeup, ideology and alliance structure, which a calculated American policy can exploit.

Obviously, this design is built on a common Republican critique, and not only a Republican critique, of the deficiencies widely perceived in Jimmy Carter's policy. Yet if it has promnise, it also bears risks. The Reagan design assumes a world of clear edges and sharp hues. It is premised on a particular hopeful model of Soviet behavior, one holding that the Soivet Union, rather that rising to the challenge, will blend to it. It is so far heavy on stick, short on carrot -- carrot in the sense of the benefits of specific agreements and of holding open a place for a Soviet world role. It presumes the United States will be quite successful in dealing with its allies and in managing conflict and change in the Third World. It presumes, too, that the Reagan domestic economic plan will work well.

The administration is entitled to its own design on the Kremlin. The rest of us are entitled to be assured that the administration is proceeding with its eyes open. Some part of that assurance can be given in words but much of it can be given only by actions over a period of time. It has not been provided yet.