In the twilight of his 24 years as absolute ruler of the Soviet Union, Joseph Stalin summoned two of his closest lieutenants, Nikita Khrushchev and Anastas Mikoyan, to his summer villa.

Stalin, then 71, knew that his health was failing and that his demise was imminent, either from natural causes or, as he constantly feared, at the hands of disloyal followers. As Khrushchev recounts in his memoirs, after a brief stroll Stalin turned to his two long-time aides, whose own loyalty he could count on only as long as he retained absolute control over their fate. "I'm finished," he said. "I trust no one, not even myself."

Now, nearly 30 years after Stalin's death, the Soviet Union again is undergoing a succession crisis. Again an aging leader, apparently determined to rule until death, clings to his job. While Leonid Brezhnev, 75, has recovered sufficiently from his latest physical setback to appear publicly, Kremlin analysts agree that his subordinates already are engaged in a largely unseen but unmistakable struggle to take his place. The charged atmosphere of physical terror that permeated Stalin's world is gone; the intrigue, deceit, paranoia and uncertainty remain.

To most Western analysts, the succession process is one of the abiding weaknesses of the Soviet system. The innate caution that Kremlin leaders operate under because of their fear of overthow, the instability that wracks the system whenever succession is under way, the constant power struggle that transforms colleagues into jealous rivals -- all contribute to a rigidity that undermines the system. Brezhnev and his cronies, ex-Stalinists all, came to power in wake of 1930s purges and still understand the ground rules of Kremlin power as Stalin laid them down.

Like Soviet rulers before him, Brezhnev has spent his time in office accumulating power at the expense of potential rivals. He has purposely avoided grooming a successor in large part, American experts say, because he feared an heir would inevitably turn into a challenger -- the way he himself did when he overthrew his own sponsor, Khrushchev. He has surrounded himself increasingly with cronies and family members, avoided decisions that might alienate some of the powerful interest groups whose support he commands and bottled up the aspirations for power of a younger generation of Soviet leaders.

When he dies or is forced out, many analysts believe, the gray men of the Kremlin will come alive in a struggle for power unmatched since Stalin's death. If the Stalin precedent holds, thousands of careers will be destroyed, loyal Communists and experienced bureaucrats will be consigned to permanent oblivion, as leaders compete in a burst of raw individualism that belies the Soviets' own view of their government as a steady, impersonal machine of history moving toward an objective goal.

The struggle will occur against a backdrop of domestic problems that analysts say are the harshest and most difficult the Soviet Union has faced since World War II and that may pose a threat to the very survival of the Soviet system. These problems will have profound impact on the succession process and may prove critical in determining its winner. All who compete for a share of the Soviet Union's shrinking economic pie -- the military, those who run the huge agricultural and industrial sectors of the Soviet state and those who represent the great nationalities and republics -- will play a role.

"It will be a very messy, prolonged and bitter struggle, much like the Stalin succession; there will be open conflict between the new leaders and their opponents on fundamental issues," said Seweryn Bialer, director of Columbia University's Research Institute on International Change.

Most analysts see a two-phased succession, with Brezhnev's aging cronies holding the status quo for a limited time, followed by the real battle among younger, aggressive challengers. "There's good reason to suspect surprises," said Myron Rush, Cornell University Soviet scholar and adviser to the CIA. "No one's a candidate and therefore everybody's a candidate. My hunch is it will be a prolonged succession and a golden opportunity for someone smarter, more vigorous and more brimming with ideas to take control."

The one unchanging rule of Soviet succession is that there are no rules. Nothing is written and there is no mechanism for the smooth passage of power from one leader to the next.

"The 'game' of politics that has replaced the former Mafia-style struggles for power is no longer murderous, but it is still not a stable game played with an established arena, according to accepted rules," wrote Zbigniew Brzezinski before he served as Jimmy Carter's national security adviser. "It resembles more the anarchistic free-for-all of the playground."

The Communist Party's general secretary, held to be the country's key position, generally has been chosen in a closed meeting of the ruling Politburo, which has 14 full members. That choice is then ratified by the party's 319-member Central Committee. But even this process is at best uncertain. While the general secretary's post is a key one, there is no guarantee that the man who holds that post will in fact rule the Soviet Union. Also, decisions of the Politburo are not necessarily final. In 1957, Khrushchev's enemies on the Politburo (then called the Presidium) voted 8 to 4 to oust him. But Khrushchev rushed enough Central Committee supporters to Moscow to overrule the decision.

Past leaders have proven not only unwilling to transfer authority, but unable to do so. Lenin, crippled by strokes and near death, sought to ensure power would be shared collectively by his survivors. Instead, Stalin, the man Lenin most feared and warned his fellow Communists against, emerged victorious. Stalin so feared his own subordinates that he killed off many of them as soon as they reached a position of power. Khrushchev dismantled much of Stalin's terror network and scorned his predecessor's paranoia -- only to be overthrown by his own emboldened subordinates.

Then there is the utter unpredictablity of who will win and how they will govern. Few would have predicted that Stalin, the brooding dark presence whom Leon Trotsky in 1917 described as "a dull, small-town mediocrity," would outmaneuver and crush Trotsky. It seemed unlikely that Khrushchev, one of Stalin's colorless henchmen, a largely anonymous party hack of little education or sophistication, would emerge victorious over Stalin's own presumptive choice, Georgi Malenkov. Even more unlikely was the notion that Khrushchev not only would attempt to massively reform the Soviet state but renounce and vilify the master he had served so faithfully and supposedly had revered.

Critics argue that the succession process rewards mediocrity, that no one wants to stand out from the crowd for fear of attracting the wrong kind of attention. It also rewards deceit. At the height of their power struggle, Khrushchev used Malenkov's call for liberalization and peaceful coexistence to enlist support from more orthodox elements of the Communist Party against Stalin's presumptive heir. But within months of his triumph, Khrushchev himself began to adopt similar positions. Six months before the coup against Khrushchev, Brezhnev and fellow conspirator Mikhail Suslov publicly hailed the man they planned to overthrow as the ultimate Marxist-Leninist hero.

"It's so hard to tell what these guys really are thinking," said Jerry F. Hough of Duke University and the Brookings Institution. "Stalin's chief lieutenants were Khrushchev and Malenkov and if he'd known what they really thought of him he'd have killed them both."

Leonid Brezhnev long was considered one the grayest of the Kremlin's bureaucrats. His role in Khrushchev's ouster in 1964 was seen as part of a collective effort carried out by a large majority of the ruling Politburo who saw Khrushchev's domestic policies as economically disastrous and who feared his reformist impulses ultimately could cost them their jobs. Brezhnev's early rule was in large part based on his promise to avoid the one- man rule, bluster and cult of personality that were Khrushchev's trademarks.

But a new view of Brezhnev has emerged in recent years. The man who negotiated arms limitation agreements with Presidents Nixon, Ford and Carter and talked of his commitment to world peace also presided over a massive arms buildup that at the least has won the Soviet Union strategic parity with the United States. The man whose ascendancy was a triumph of collectivism has amassed and consolidated his personal power to the point where many Sovietologists now concede they underestimated both Brezhnev's drive and his ego.

"Brezhnev is a great egotist with a will to power that seems relentless," said Cornell's Rush. "This is a man who gave up smoking at age 70. I don't think he can let go of the job."

Most Kremlinologists define the Brezhnev era as the period beginning with Khrushchev's downfall and ending around 1977, and many have judged that era, in Bialer's words, "the most successful period of Soviet international and domestic development." But most believe that Brezhnev has lingered in power for too long and that his legacy has turned sour over the last five years, especially on domestic matters.

Throughout most of the 1970s, Brezhnev was credited with keeping the patchwork economy functioning adequately through a cautious, conservative approach that emphasized consensus among the Soviet Union's various major interest groups even while pouring billions more rubles into the military. But in recent yeas his economic balancing act has come apart and the verdict of many analysts is harsh.

"This is a regime that has temporized and stalled out on every domestic issue, said Arnold Hoerlich, a Rand Corporation Soviet analyst. "The old leadership has mortgaged the country's future."

The economic problems that the Kremlin's new leaders will inherit pose a delicate balancing act. Whoever aspires to power must offer a domestic economic program that attempts to come to grips with the problems while at the same time enlisting support from the powerful interest groups that hold at least a veto power over selection of the new leader. Analysts say they have few clues as to who will triumph, but they are convinced that policy issues will be key weapons in the succession battle.

One almost certain result, they say, is that Brezhnev's successor will quickly find himself under pressure to renounce his predecessor. This is a time-honored ritual in Kremlin politics, one which only Lenin so far has escaped. Stalin never renounced the founder of the Soviet state, but he discredited Lenin's wife and ruthlessly purged virtually every Lenin ally and crony. "I remember her as a broken woman," Khrushchev wrote of Lenin's widow. "People avoided her like the plague."

Khrushchev's renunciation of Stalin in 1956 was a key element in his final triumph over Stalin's heirs. Khrushchev himself was consigned to political oblivion following his own ouster. Brezhnev never mentions Khrushchev publicly and the former leader's name disappeared entirely following the 1964 coup until 1970, when Pravda printed his shrewdly worded disavowal of his memoirs after they were published in the West.

Khrushchev "was transformed by his former colleagues, some of whom owed everything to him, into an unperson. He might never have existed," wrote Soviet scholar Edward Crankshaw in his introduction to the memoirs.

Brezhnev's image is unlikely to escape similar abuse at the hands of his successors, analysts believe, in part because tradition appears to demand it and in part because of his perceived mishandling of the economy. "It's even money that five years from now Brezhnev will be seen as the villain," said Hoerlich.

Many Kremlinologists predict that Brezhnev's belated heir, Konstantin Chernenko, will be forced to distance himself from his sponsor quickly or else face a possibly unsurmountable obstacle to power. Indeed, many analysts suspect that despite his apparent status as front-runner, Chernenko will fade almost as soon as Brezhnev leaves the scene.

"Brezhnev's domestic policies will come under attack as soon as he goes and the guy left carrying them out will be very vulnerable," said Rush. "In essence, he'll be stigmatized by Brezhnev's support."

Whoever wins, most analysts agree, the Soviet Union's immediate future looks grim because of its declining economy. Hoerlich is one of several experts who believes the issues up for grabs go to the heart of the Soviet system: Having transformed the country from an agriculture-based 19th-century state to an industrial giant, can it now bring Russia into the 21st century of sophisticated "intensive" development?

Most believe the swollen, immobile bureaucracy that oversees the Soviet Union is incapable of real reform. "The entire system is adverse to innovation," said Angela Stent of Georgetown University. "You get no rewards for it. In fact, you get penalized."

Former deputy national security adviser William Hyland agrees. In a recent issue of Foreign Affairs, he predicted: "One can foresee a leadership more or less tied to conservative elements, doomed to maneuver within narrow limits, caught up in an economic crisis but unable to adopt policies that would constitute a decisive solution."

Even if the reformers should win, analysts doubt Soviet policy will turn liberal or benign. Most believe that an innovative new leader who could muster support for cutting back on military growth might be willing to curb adventurism in the Third World, but would likely feel compelled to appease the Kremlin's hard-line factions by maintaining even tighter control over the Soviet Union's own citizens and the bordering areas. Said a State Department analyst, "A Soviet regime busying itself with domestic problems may be willing to cut far-flung commitments of the empire yet really crack down on Afghanistan and Eastern Europe."

The military has played a subordinate but nonetheless important role in past successions. In 1953, Khrushchev and other Kremlin leaders turned to World War II hero Marshal Georgi Zhukov for armed support in engineering the arrest and execution of their most lethal rival, Lavrenty Beria, head of the secret police. In a scene out of a Hollywood gangster movie, Zhukov and his generals, their pistols drawn, interrupted a Presidium meeting at the Kremlin to seize Beria after being secretly summoned from an adjoining room.

Zhukov also played a key role in Khrushchev's consolidation of power in 1957 by locating and flying to Moscow Khrushchev supporters on the party's Central Committee for a showdown vote -- only to find himself ousted four months later for "Bonapartist aspirations." Leaders of the armed forces eventually felt betrayed by Khrushchev's cuts in defense growth, and they quietly withdrew their support for the Soviet leader, paving the way for the 1964 coup.

This time, some analysts suspect more intensive involvement as the marshals seek to guarantee their budget and prerogatives. A few even see a martial-law-style government based on the Polish model. But the majority view is that Poland, with its weak Communist Party apparatus and anti-Communist nationalistic tendencies, is a long way politically from the Soviet Union, where the party is strong and where there is no open conflict between communism and nationalism, at least in the dominant Russian republic.

These analysts instead see the military, as well as the KGB, picking among civilian candidates and allying themselves with the ones who will assure them of continued support. "At a minimum the armed forces will continue to lay claim to the same share of the pie," said Coit D. Blacker, special assistant on security matters to Sen. Gary Hart.

While the analysts can describe the men and forces that compete for power in the byzantine world of Kremlin politics, few are willing to predict the victor. Indeed, the most knowledgeable appear to be those who most quickly admit they lack the basic information needed to make an intelligent guess. One State Department analyst recalls then U.S. ambassador Charles Bohlen's comment to an embassy aide who after Stalin's death complained that the Kremlin's men all looked alike.

"Yes, they all look so gray and homogenous," replied Bohlen, "but we have no idea what goes on underneath the surface. Worlds are colliding down below."

By Glenn Frankel; Glenn Frankel is an assistant foreign editor of The Washington Post.