If words can define an era, then perestroika is the catchword here before Tuesday's opening of the Communist Party Congress as Soviet leader Mikhail Gorbachev enters a decisive phase of his leadership.

Literally, perestroika means rebuilding, but in the Soviet Union's current political climate, it has taken on a broader social connotation. Appearing almost daily in speeches and in the press, the word now sums up a range of new themes: openness, honesty, the need for harder work, more personal initiative, less talk and more action.

In short, it has come to signify a psychological readjustment, a new state of mind fundamental to Gorbachev's hopes for the revival of Soviet society.

The concept of perestroika will dominate next week as the 27th Congress of the Soviet Communist Party opens here. Yet it is still not clear to what extent the word represents a real break with the past, or is simply the latest in a long string of Soviet slogans.

And despite the buildup and historic significance of next week's gathering -- expected to be the most lively and interesting party congress since the days of leader Nikita Khrushchev -- few here expect this basic question to be decided at the congress itself.

"A congress is not a place where things happen. It is where they get the seal of approval," said one dipomat. "And my sense is that at this one, we will not see an unveiling, but more a clearing of the decks."

The party congress, an event that takes place once every five years, comes at a fortuitous moment for Gorbachev. One year after assuming office, he has been given the chance to appoint the country's top leadership through nominations to the powerful Central Committee. Expectations are that he will name new people to at least half of the committee's approximately 300 positions.

He will also present a revised program for the ruling Communist Party, the first since 1961, as well as a five-year plan for the national economy. And his speech to the congress Tuesday is expected to be his most significant to date, as well as the high point of the meeting.

Like most occasions in Soviet life, the congress will be carefully scripted, serving to ratify publicly decisions already made in private.

By the time the congress opens Tuesday, Gorbachev will have already accomplished much of its work. His team is largely in place, the groundwork is laid.

"He's like the manager of a failing football team who has gone out and bought new players. Now they have to get out there and play," said one western analyst.

Few analysts expect the announcement of any major shift in Soviet policy, either on the domestic or the foreign policy front. In the international arena, Gorbachev made a major disarmament proposal Jan. 15 and he is unlikely to make any further initiative.

On internal affairs, which are the new leader's main concern, he is not expected to come down on one side or the other of the debates now raging in the media on such issues as allowing some services, like auto repairs, to be provided privately by individuals, adjustments in the pricing system to reflect supply and demand and other economic changes.

One economic experiment, involving self-financing at a machine-building factory at Sumii in the Ukraine, may get a favorable mention by Gorbachev or by Premier Nikolai Ryzhkov, but probably only in generalities.

"There may be a bow in the direction of some shifts, but now is probably not the time for anyone to ram an economic blueprint down the throats of the delegates," said one western diplomat.

In his first year, Gorbachev moved rapidly, and with far more assurance than anyone expected. From the Politburo on down to the regional party level, he removed an older generation of Soviet leaders, and replaced them with men who resemble himself -- in age, in qualifications and in dedication to the "new style of work."

At least 45 of the 159 regional party secretaries have been replaced since Gorbachev became party leader, as have more than 40 of the 113 officials of ministerial rank.

The turnover in personnel has so far showed Gorbachev's political skill. In sparing some of the old guard on the Politburo, like Ukrainian party boss Vladimir Shcherbitsky, he seems to be reserving his strength for other battles. In toppling Moscow party boss Viktor Grishin, he has sent a message that drastic measures will be taken when necessary.

The shuffle of personnel has been accompanied by various themes, of which perestroika is perhaps the most central. The push has been not only for younger people, but sober people, qualified people, people who reject the kinds of "negative tendencies" of the late 1970s that were poisoning Soviet society.

The new generation of party leaders -- many of them presumably evaluated by Yegor Ligachev, the party's number-two man and perhaps ideologically the toughest of the new Kremlin leaders -- have come in on a wave of puritanism. Besides the national antialcoholism campaign, which has recently been given a new boost in the press, there is official scorn for all forms of self-indulgence, from flattery and sycophancy to ostentatious living.

The most remarkable example was the publication in Pravda recently of letters calling for the abolition of special shops and special hospitals reserved for party and government leaders. These privileges were widely known, but had never before been mentioned in print here.

The publication in the Communist Party paper sent a shock wave through the elite here that was softened only slightly two days later when Pravda hastily noted that not all leaders abuse their positions.

The attacks on complacency, privilege and toadyism have amounted to a broadside against the last years of the era of the late Leonid Brezhnev. That theme, which has been building lately, is expected to peak at the congress, although many consider it unlikely that Gorbachev will attack Brezhnev by name.

Rejecting the immediate past is a Soviet tradition. Khrushchev attacked Joseph Stalin, and excised him from Soviet official history. Later, the same happened to Khrushchev.

The break with the Brezhnev era has been a subtler process, but its implications are just as serious. In sweeping out the Brezhnev era, Gorbachev has thrown out the arrangement that had isolated the Soviet leadership from the people.

Bureaucrats and party people have already felt the heat.

Perestroika for them has been a nerve-wracking change, as they watch sinecures being abolished and wayward colleagues being attacked by name in the press.

Gorbachev appears to be seeking a balance between stability and change. His first move was to get rid of the older generation, a process that was helped by their advancing age.

Now the harder task is for him to establish a system that somehow institutionalizes the process, that allows a turnover of leadership without requiring major political displacement at the top.

Various options have been floated: a retirement age for party officials, limited terms in office and more democratic methods of picking high party officials. One radical suggestion that surfaced in the newspapers recently proposed that party members be considered equal with nonmembers before the law, an idea that would get to the heart of the party's special status.

How far the new leadership will want to go with this type of change is not clear. For Gorbachev there is a risk in tampering with such politically sensitive areas as party privileges.

Given the heavy load already put on the Soviet system by Gorbachev's changes so far, few expect him to rock the boat further.

"If I were he, in the middle of this process of changing people, I think I would take up the question of privileges a little later," said one senior western diplomat.

But, cautioned another, "The changes so far have been so rapid and awesome that we could always be in store for more surprises."

Next: The stakes for Gorbachev