The following imaginary memorandum from a group of expert advisers to the new leader of the U.S.S.R. is not circulating in Moscow, but perhaps it should be.

DEAR YURI VLADIMIROVICH:

We are deeply grateful for this opportunity to express our views on some of the tasks before you. First, it is our duty to acknowledge that while your election as general secretary has certainly positioned you well to exercise leadership, there is a real possibility that not only your individual decisions, but also your hold of power can still be challenged.

After all, it was Georgi Malenkov who was appointed to replace Stalin, and we do not need to remind you how long it took Khrushchev to remove and humiliate him. Even if Konstantin Chernenko is neutralized, you must remain vigilant. If the politburo senses that you are vulnerable, there will be numerous contenders to replace you.

You must identify the fundamental needs of the country and the yearnings of the central committee. The key is to reassure your colleagues that you are going to treat them with respect, that you appreciate their preoccupation with stability, that you will not promote harebrained schemes, but that you will make needed changes. If we read the central committee's mood correctly, it may be summarized as fearful of radical departures, but anxious for measured reforms. This is a contradictory message that calls for an extremely delicate balancing act on your part.

We do not have to tell you that the political mandate you have received is very different from the one given to Leonid Brezhnev in 1964. After decades marked by Stalin's cult of personality and Kruschchev's perpetual but ill-conceived reorganizations, the central committee then wanted continuity, order and calm. Now we detect a mood of impatience and even outrage among the many influential comrades who became frustrated with Brezhnev's inability to act in recent years. In picking you over Chernenko, the politburo was signaling its unwillingness to tolerate several more years of Brezhnevism without Brezhnev.

Nobody, of course, wants to change the basic line of the party. Though things went sour in his last years, Brezhnev's early successes are remembered with satisfaction and pride. Most Central Committee members are afraid of sharp turns. So do not change the course -- adjust it.

Remember that time is short. What the Politburo tolerated with Brezhnev it will not take from you. He was well-entrenched before his health began to deteriorate, and had already accomplished a great deal. But you are already 68, Yuri Vladimirovich, and your health is not perfect. Moreover, our problems are such that without quick action, your first years in power could turn out to be anything but successful.

In his last months Comrade Brezhnev was criticized for his inability to define choices and to make decisions. Responsible officials naturally appreciated that the general secretary was considerate of their interests and accommodated their views. But when you try to please everyone, it becomes difficult to develop firm and consistent policies.

You should procede on the assumption that the central committee will allow you considerable freedom of maneuver to enable you to carry through collectively reached decisions, even if they disregard some parochial interests and upset some influential comrades. On the other hand, you should not appear to be too ruthless. Ideally, you want to be firm, decisive and fair.

Initially your leadership will be measured by your success in dealing with your most pressing problem, the economy. But it will be politically and psychologically difficult to break traditional structures and patterns.

Granting the difficulty of funamental reforms, we propose that you begin with several quick fixes. They will not remove the underlying problems, but they will buy you time and perhaps some popular recognition.

Waste, corruption and red tape have reached embarrassing levels. Vigorous clean- up efforts could save billions of rubles, remove some bottlenecks and send several embezzlers to jail -- to the immense satisfaction of the people. However, a sense of proportion is important. An all-out campaign against corruption would terrify the central committee, particularly coming from someone with your KGB credentials.

You will subsequently have to address two other great deficiencies -- over-centralization and lack of discipline. As you know better than we, the Hungarian experience can teach us a great deal. But the size of our country, the scale of our economy and the much higher priority we must give to defense argue against a slavish replication of the Hungarian model. Also, we have to admit that the Soviet work force does not consist of Hungarians. In the same conditions, too many of our workers, farmers and -- especially -- managers are likely to act with less motivation and responsibility than their Hungarian counterparts.

Decentralization of the economy requires greater autonomy for industrial and agricultural management. But the first thing the managers will demand is the right to determine the size and composition of their work forces. Millions of people would be fired, creating an unemployment problem for the first time since the 1920s. This would anger provincial party officials who want neither to lose control over economic decision-making nor to have to deal with the unemployed. They are also unlikely to welcome the rise in crime, drunkeness and popular discontent that would surely follow. Meanwhile, it would take years for the reforms to bear fruit; you would come under great pressure from the party apparatus and the people to abandon your policies before they have had time to work.

Consequently, you must find a way to begin decentralization of the economy tactfully and gradually. Decentralization must be accompanied by well-thought-out labor relocation programs. The newly unemployed must be encouraged and, if necessary, forced to move to Siberia where we badly need more workers.

The need for discipline requires continued vigilance regarding manifestations of dissent. At the same time, we do not need to be unnecessarily strict with artists and intellectuals. Why not permit the artists to experiment with shapes and forms? And the scientists, who are so important to us, might respond well to some kind of olive branch -- perhaps releasing Andrei Sakharov from Gorky. But those who challenge the very foundations of our state and who are willing to appeal for help to our foreign adversaries must be dealt with forecfully

Patriotism, discipline and order are the by- words of any possible coalition supporting economic reform. You will need more than an endorsement from managers, scientists and intellectuals. You may look to the military for that extra, essential support. Fortuntely, Comrade Ustinov knows from his many years in the defense industrial complex that a sick economy cannot in the long run support a strong military. The marshals and generals may not instinctively support reform, but they are pragmatic and you may be able to convince them there is no other way out. But to keep them on board, you will have to demonstrate that defense expenditures can remain high and that patriotic values will not be undermined by an irresponsible tolerance of nihilism and pacifism.

Serious problems face us in foreign policy as well. But none of them is as pressing as our domestic troubles, and there are also some encouraging opportunities.

You have done well to begin by pursuing reconciliation with China. We have overestimated the Chinese threat. The new leadership in Peking is not engaged in a major military build-up and their forces are increasingly inferior to ours technologically. They have, however, successfully tested their first missiles launched from a submarine; those missiles drastically limit our military options. China shows and clear signs of disillusionment with the United States, giving us an historic opportunity to shift the correlation of forces in our favor.

China has presented us with four demands: withdrawal from Afghanistan, Vietnamese withdrawal from Kampuchea, the removal of our troops from Mongolia and a reduction of our forces on the Chinese border. These represent Peking's initial bargaining position. Unlike earlier Chinese territorial claims, these points can be addressed in the context of a general settlement. It may be in our interest to give them serious consideration.

We need to reassess our Third World commitments. It should be taken as a given that the Soviet Union is a great power with global interests and influence. Still, as you know, we have sometimes become overextended, getting involved in situations from which there was no way out. There is no contradiction between being assertive and calculating costs and benefits.

Afghanistan may be a good place to start. Of course, a withdrawal would damage our prestige and make it hard to maintain Babrak Karmal in power or even in a coalition government. But having decided against attacking sanctuaries in Pakistan, we have no prospects for winning a military victory. Is it worth continued enmity with the Chinese to prolong a no-win situation in Afghanistan? Every opportunity for a solution there should be explored with Pakistan, China and possibly India and Iran. If we could find an acceptable way to resolve the Afghanistan problem, the benefits in our dealings both with Asian neighbors and with other non-socialist countries, particularly in the Moslem world and Europe, could be enormous.

Kampuchea is another case calling for innovative thinking. The Vietnamee would never agree to returning Pol Pot to power. Prince Sihanouk may be a different matter. He is flexible and willing to cut a deal with Hanoi. If necessary, we will have to apply pressure, for we cannot continue to allow Vietnam's parochial interest to sabotage our global policies.

Finally, if we manage to improve our overall relationship with Peking, we should have little fear of withdrawing troops from Mongolia or reducing our forces on the Chinese border. Actually, thinning our forces in the East can release manpower and funds for weapons procurement; both are priorities with Defense Minister Utinov.

Rapprochement with Peking would also free up some of the SS-20 missles we currently have targeted on China. We might then propose to the NATO countries that we significantly cut our SS-20 forces if the Americans drop their plans to deploy new missiles in Europe. Of course, Reagan will not agree, but the Europeans will be interested. They could either force Washington to accept our proposal or refuse to deploy new U.S. missiles.

Generally, our relations with Western Europe are on the right track. Eastern Europe is a different matter. Our Warsaw Pact allies are increasingly dependent on our subsidies and are domestically unstable. They must be allowed more internal autonomy to avoid further unraveling of the socialist system. As long as the East Europeans remain loyal and keep socialist regimes safely in power, we need not insist on ideological conformity.

Gen. Jaruzelski and his associates may not satisfy all our definition of good communists, but they know their local circumstances and have managed to keep things under control. Putting excessive pressure on them to comply with our views may be counterproductive.

Finally, we have the Americans to deal with. Rarely have relations between our two countries been at such a low point. While actively supporting national liberation movements, Brezhnev was careful not to challenge American vital interests directly. Whether or not our activities in the Third World have been wise, the United States has no right to punish us for them.

The trouble began when they broke the promises made by Richard Nixon and refused to give us credits or Most Favored Nation trading status, insisting that we make public concessions on our own emigration policies. They failed to ratify SALT II, as well as two other nuclear testing treaties, and they broke off several sets of arms control negotiations. They imposed a grain embargo and then pipeline sanctions. And now the Reagan administration is actively studying ways to promote "democracy" in the Soviet Union -- in other words, looking for ways to destabilize the Soviet system.

We know that Reagan and his men will never willingly accept us as a superpower. We know too that their one-sided arms control proposals are a screen to hide their efforts to regain military superiority. We must continue exposing their insincerity on arms control and take prudent steps to make sure that the United States fails to achieve even the illusion of a first strike capability.

Yet, even with Reagan, there may be some opportunities to explore in our relationship with the United States. Reagan and his advisors do not know what they want from the Soviet Union, so perhaps we should try to impress them with "concessions" we intend to make anyway. Compromise on Afghanistan, flexibility in Kampuchea and more generous proposals at Geneva negotiations on European missiles might not satisfy the American administration but they could make it more difficult for the president to continue his hysterical crusade against us.

We should also not forget that there is a difference between what Reagan wants and what he can realistically expect to get from Congress. And when U.S. defense spending is cut to reduce the budget deficit, the Americans will face a choice between negotiated arms control with us, or the prospect of both no agreements and no weapons.

We cannot predict how Reagan will behave if confronted with such a dilemma. But Soviet diplomacy should neither let the president off the hook and or provoke the American people to rally around the flag.

We should be tough but statesmanlike. Certainly, the United States must be taught a lesson. But excessive confrontation will not only draw down our resources, it will also force the Europeans and others to take sides, possibly against us. In short, our advice is to avoid too accommodating a stance, but keep a door open for a better tomorrow. If we play our cards right, Reagan will have to adjust or fail: Let Reagan be Reagan and he will hang himself. We will not even have to provide the rope.