HARD AS IT may be for Americans to believe, the death of Leonid I. Brezhnev is unlikely to bring any early or dramatic changes in Soviet policies or Soviet-American relations. This is true because -- alas -- the Soviet Union is so profoundly different a country than we are used to.

We have already heard prominent Americans predicting that the transition period will be a time of Soviet militarism, or a good moment for a peace offensive, but all such predictions are improbable. Forecasts of sudden change in Russian policies can only be made by outsiders who project their own patterns of behavior onto the Russians.

In America a new president sweeps clean the slate of state: New officials blithely implement new policies (often contradicting the old ones) as though history began the day they took office. The West European democracies are more consistent, but they, too, can switch directions abruptly.

Not the Russians. Apart from the Bolshevik Revolution itself, changes of government in Russia have been marked not by departures but by a striving for continuity, at least for a couple of years. Yuri Andropov will not ignore that tradition.

From a Russian point of view this makes eminent sense. The challenge to Andropov and his colleagues is to preserve a claim on legitimacy by reassuring the people that they will keep the historic bargain between Russians and their rulers. This bargain is simple: The people give up any right to chose their leaders or influence their policies (in other words, they give up any claim to freedom) in return for basic security, order and the staples of daily life.

An abrupt change in the party line would only raise doubts that the new leaders could make good on their end of the bargain. Abrupt changes would rekindle the ancient Russian fear of disorder or anarchy. So the new Soviet leaders will try to avoid abrupt changes.

This does not mean a new Soviet government is bound to stick forever to the path set in the Brezhnev era. On the contrary, the many grave problems, domestic and international, that the Soviets now face will require significant policy changes in the years ahead. But changes will not come in the years immediately ahead. They are likely in the mid-1980s and beyond.

The money men on Wall Street talk about the way the stock market "discounts" a big event before it takes place -- an election, a new tax cut, whatever. In a similar way, both the Soviet elite in Moscow and the rest of the world have already discounted the death of Leonid Brezhnev. Like Konrad Adenauer or Mao Tse-Tung, Brezhnev was one of those fixtures on the international stage who actually prepares the world for their eventual departure by defying the actuarial tables and sticking around so long.

In Moscow, maneuvering in preparation for the end of the Brezhnev era has been going on for years. The committee that has been running the country for the last 18 years has had to jigger its membership as others of the old men at the top have died or retired, and lately the jiggering has suggested that the committee was preparing for the post-Brezhnev era. The quick selection of Andropov on Friday as the new general secretary of the communist party indicates that the ruling committee has known where it was headed for a long time.

The crucial point here is the existence of that committee. For all the eagerness of the news media to make Brezhnev into a personal dictator, he has never been one. He has always shared power -- willingly, by all appearances -- with others in the group who conspired with him to oust Nikita Khrushchev (who really was a personal dictator) in October 1964.

The record on the committee's importance is clear. That record is sprinkled through Richard Nixon's and Henry Kissinger's memoirs of the l972-74 period when detente was in bloom, and all important matters in Soviet- American relations were referred to the Politburo for final decision. In 18 years as the leader of the Soviet Communist Party, Brezhnev never gave an extemporaneous speech. He invariably read from a prepared text -- a text presumably approved by the Politburo.

Recently, when Brezhnev reportedly could work no more than a few hours a day, the committee was obviously running the country without him -- as it will be running it now.

Andropov was an important member of the committee in the Brezhnev era, particularly since 1967, when he was sent to the KGB to handle a top-priority matter for the leadership: the reassertion of strong controls over unorthodox political behavior. Andropov must have become a hero of sorts to the committee when he managed -- over more than a dozen years, with patient diligence -- to wipe out the phenomenon of political dissidence that arose in the '60s. Dissidents terrified the committee, because they seemed to challenge its legitimacy, its right to rule in the name of the people. Thanks to Andropov, today there are virtually no dissidents.

The cardinal achievement of the Brezhnev era was to broaden the Soviet regime's base of active support. When the Brezhnev group took over in 1964, a relatively small Soviet elite benefited personally from the system. During the years that followed the system of privileges and special rewards for members of the elite grew dramatically, as did the size of the elite that was eligible for them.

By giving hundreds of thousands and probably millions of people a direct personal stake in the system -- a stake based on improved housing conditions, better food to eat, opportunities to travel abroad and the like -- Brezhnev enhanced the stability of the Soviet regime.

But there was a downside to that accomplishment. By creating such a large group with a personal stake in the status quo, Brezhnev made it terribly difficult to alter the status quo. Thus it turned out that all the Brezhnev group's attempts at reform, particularly of the Soviet economy and agriculture, came a cropper. A vast layer of the Soviet establishment just wasn't interested in reform.

This inertia is not something a new leader can abolish with a wave of his hand. It is now a fact of Soviet life, and it will remain one for years.

Whether Andropov will even want to challenge this inertia remains to be seen. At 68, he is already six years beyond the life expectancy for a Soviet man. He has reportedly suffered from heart trouble. Many Kremlinologists expect him to be a transitional figure who will prepare the way for a member of the next generation, someone now in his 50s, to preside over the next phase of Soviet history.

But even if Andropov wanted to make a strong individual mark as leader, history suggests it will take him several years to be able to try. Three years after the Brezhnev group took power, the Soviet spokesman at a Soviet-American "summit" meeting in Glassboro, N.J., was Alexei N. Kosygin, not Brezhnev. After Stalin died there were several years of tumult inside the ruling committee before Khrushchev emerged on top. The committee moves slowly when deliberating policy departures, and it takes time for one man to consoldiate a position of personal ascendancy.

Even Brezhnev, who indisputably did achieve personal ascendancy within the committee, apparently never had the personal power to impose a significant policy change on his colleagues. He built a consensus on the committee for his detente policy, but he didn't dictate it. His greatest personal power may have been negative. According to one intriguing story that is told by well-informed people in Moscow, Brezhnev did personally prevent a Soviet invasion of Poland at the end of 1980 -- the committee was ready to do it, but Brezhnev denied his colleagues the consensus they required for such a big step. It's just a rumor, but a plausible one.

That there will be change in Russia is inevitable. The '80s may prove to be a decade of abrupt discontinuity in Soviet history. A generation gap has emerged in the Soviet Union -- the Russians may be about to have their version of the '60s. The economy has stopped growing, agriculture is deteriorating, and the system of control in East Europe is no longer effective. These are grave problems, and none can be dealt with effectively with the kind of marginal policy adjustments that typified the Brezhnev era.

At least theoretically, the Soviets' need to make changes creates opportunities for the United States and its allies. But the Reagan administration seems committed to pursuing a confrontational policy toward the Russians, rather than exploiting new opportunities for different kinds of approaches.

President Reagan's decision not to attend Brezhnev's funeral can be defended on numerous grounds, but there is no doubt about how the Soviets will interpret it: as an affront. If the American president is not interested in attending a Soviet leader's funeral, he obviously isn't interested in a better Soviet-American relationship -- that will be, understandably, the Soviet view.

The Reagan policy until now could be described as the "uncle" policy -- the United States is going to put so much pressure on the Soviets that they will eventually cry uncle, agreeing to American terms for arms reductions, agreeing to withdraw from Afghanistan, agreeing to grant more human rights to Soviet citizens and Poles.

The chance of this approach succeeding was always slim; with new leaders in the Kremlin it is nonexistent. The most obvious thing new leaders cannot do under any circumstances is to begin acceding to the demands of "imperialists," as they like to call us. No signal would be more threatening to the Soviet elite than a hint that their new leaders can be intimidated by the United States.

So, ironically, American policy will reinforce the Soviet tendency not to change course in the aftermath of a change of leadership. There are no prospects in the forseeable future for a better East-West relationship.