Should President Carter invite Leonid Brezhnev to a summitt meeting? Brezhnev, it is argued, is too weak physically and therefore politically to make such a meeting worthwhile. The struggle for the succession, it is said, is already in progress, and Carter should wait until it is resolved, and meet Brezhnev's successor, who would be eager to gain the international prestige conferred by a summitt meeting - and willing to pay a political price for it.

But if the struggle for the succession is indeed in progress, and if, as there is every reason to believe, it is concerned with policies as well as personalities, then the time for Washington to try to influence the direction of developments in Moscow is now.

A summit meeting with Brezhnev, even if he is largely a figurehead, would give Carter the opportunity to convey to the whole Soviet leadership something of the gains that could result from a favorable development of U.S.-Soviet relations - and of the dangers if no such development takes place. It would then be up to those Soviet leaders who want to make the best of the existing opportunities to take the matter up with their colleagues.

Three quite different theories have emerged in the debate among Western analysts about the future of the Soviet Union after Brezhnev. Most of the government analysts and some of the older academic experts on the Soviet Union whose opinions I have sampled assume that things will go on much as before. Some of the intelligence and academic experts believe that a turn to the right, to a more conservative and hard-line policy, is likely. And some of the academic experts (mostly the younger ones) and very few intelligence analysts, believe that a more liberal regime might conceivably follow the Brezhnev era.

I am firmly on the side of this liberal "faction" - but I would add that this prediction is likely to come true only if Western policymakers help it to come true. The most telling lesson I have learned in 28 years of analyzing the Kremlin is that there are always policy struggles going on between a conservative wing on the one hand and a moderate or more liberal wing on the other, even if the evidence of such struggles does not become available to us until much later.

The most discouraging lesson I have learned is how difficult it is to persuade the powers that be in the Western capitals, particularly in Washington, that such struggles are in progress, and that in shaping our own policies we ought to take that into consideration. That is not to say that the West ought necessarily to support one Kremlin leader against another, but that it ought to act in a way that would help the Kremlin to decide on the policies that would be to the mutual benefit of both East and West. But in Washington, domestic political reasons often prevent the pursuit of policies that would take such struggles into account. When Winston Churchill proposed to President Eisenhower after the death of Stalin a summit meeting with the new Soviet leaders, Secretary of State John Foster Dulles advised firmly against it - and a rare opportunity to devise a new relationship with the Kremlin was lost. Only later did it become generally accepted that one of the Kremlin factions had wanted at the time to develop a more cooperative relationship with the West. There have been several other such missed opportunities since then.

Sometimes the failure to act on such opportunities is due more to a failure of analysis than to a failure of Western policy. The present majority view that a conservative regime is more likely to prevail after Brezhnev is based on a number of assumptions. One is that the Soviet leadership is committed first of all to its own perpetuation - which is a view I share. But it is then argued - and this is where I disagree - that the instinct for self-preservation will make the new Soviet leaders follow the conservative policies that have helped in the past to curb dissent, to prevent political reform, to avert innovation.

I believe that is the wrong view, because there is a good deal of evidence that a new generation of Soviet leaders is emerging that holds that without innovation and reform, without economic experimentation and political change, the Soviet regime will find it difficult to retain its place as a leading power in the modern world. They are just as interested in self-perpetuation, both for themselves and for the regime, as their conservative colleagues. But they believe that their ends would be best achieved by following more liberal policies, both at home and abroad - and this is where we can help ourselves by helping them.

In the transition period that the Soviet leadership has already entered, and in the struggle for the succession to Brezhnev, which will come into the open sooner or later, these conservative leaders and their "liberal" - for want to a better word - opponents are bound to clash, repeatedly. By devising our foreign policies in ways that might help the liberals, by meeting them halfway in economic and arms negotiations - provided always that we do not thereby injure the West's basic interests - we can do a great deal to promote the kind of East-West understanding that has seemed to be almost within our grasp several times since the death of Stalin.

It is often said that those who urge the kind of policy I discuss here are personally "soft" on the Kremlin, that they would give it anything it wants. So far as may own views are concerned, this is easily refuted by the hard line I have taken so often in the face of what I have considered Soviet excesses.

For example, I believe the West should take firm action to arrest the expansion of Soviet power in Africa. If we fail to do that, we will in effect be helping the Kremlin hard-liners, for they will come to believe that they can get away with anything, and will therefore be encouraged to try even more risky adventures and to follow an even less accommodating policy in other negotiations with the West. But our resistance to the Kremlin's excesses must be part of a constructive policy designed to evolve a new relationship, one that could be opened up by the present transition to a new regime that will be represented, sooner or later, by a new generation of Soviet leaders. Above all, we must beware of missing the opportunities we have repeatedly missed in the past. One such opportunity is the proposed summit meeting between Carter and Brezhnev now being intensively discussed by U.S. policymakers.

In meeting with Brezhnev, it can be argued, Carter would be taking a hand in the Soviet succession struggle - but he could hardly be accused of backing a particular Soviet leader, or of interfering in the Kremlin his view of what the U.S.-Soviet relationship might be - and he would be doing it in good time to strengthen the hand of those of Brezhnev's possible successors who want a more cooperative relationship with the West. For once, we would be anticipating a change of guard in the Kremlin and the change of policy that has always followed it, instead of merely reacting to it after it happened.