Warning of economic catastrophe and even the prospect of Arab Spring-style unrest in the world's biggest energy producer, Lebedev painted a grim picture of Russia's future as the Kremlin prepares for the 2012 presidential election.

Prime Minister Putin, Russia's most popular politician, and his protege, President Dmitry Medvedev, have refused to say which of them will run in the election, though many diplomats believe Putin will return to the Kremlin.

Lebedev, a 51-year-old former Russian spy who made billions trading stocks and bonds after the 1991 collapse of the Soviet Union, said Putin had still not made a final decision on whether to return or to allow Medvedev another presidential term.

But Lebedev warned that popular discontent at vast corruption and the tightly controlled political system that Putin crafted during his 2000-2008 presidency was rising.

So how does he describe Putin?

"Clever. Rational enough to understand that the course he has been leading has to be changed. And that is the only hope I have," Lebedev told Reuters in almost perfect English.

"He is not de Gaulle, not Churchill, not (Soviet leader Konstantin) Chernenko, not Brezhnev, not Mugabe, not at the moment, but it might come to that. Give him another 20 years and leave it the way it is, and it will be Zimbabwe," said Lebedev.

Putin's spokesman, Dmitry Peskov, said he did not want to comment on Lebedev's opinions.

Brezhnev's 1964-1982 Kremlin rule has been dubbed the era of 'stagnation', when booming oil production masked the industrial decline that eventually brought the collapse of communism. Mugabe, once a hero for many Africans, has been criticized by opponents for holding on to power for more than 30 years and leading the country into rampant inflation and decline.

Lebedev, one of the only major Russian businessmen who has risked irony about Putin in public, said it was still too early to say what Putin's true legacy would be, but that Russia's future hinged on the will of one man.

"If you preserve it this way then he will be like Brezhnev and Mugabe, it will be an interesting sort of combination, if he doesn't change course, change his people," he said on Tuesday.

The billionaire's views contrast also with the rosy image investment bankers sometimes present of a resurgent and confident Russia with a swiftly growing $1.5 trillion economy that offers vast profits to those willing to take the risks.

Medvedev, a 45-year-old lawyer whom Putin guided into the Kremlin in 2008, has appeared to differ with his mentor in recent months, warning that Russia faced stagnation and even strife unless reforms were pushed through.

Lebedev said some felt he was either naive, foolish or playing some impenetrable game to voice such criticism in a country where the Kremlin's chief political strategist once said that Putin had been sent by God to help Russia.

"I am trying to make a very simple thing clear: If the course is not changed, this is a completely doomed economy," said Lebedev.

"I like what he says, but not a lot has been done," said Lebedev, who made his first half a million dollars trading Brady bonds in the early 1990s. Forbes says he is worth $2.1 billion, though Lebedev says that is too high.

SLAVIC SPRING?

So does Russia face a 'Slavic Spring' along the lines of the unrest that has toppled authoritarian rulers in the Arab world?

"A revolution? A demise for sure, an economic catastrophe," he said. "Clearly there are a lot of winds of change in the country, but it is difficult to say in what ways it blows."

"I hope it is going to come in a civilized way," he said.

Some might consider notions of a Russian-style "Arab Spring" overblown. Change in Russia has traditionally been driven by small elites rather than the masses. Brezhnev's order was dismantled by reformer Mikhail Gorbachev, himself later usurped by Boris Yeltsin who later passed power to Putin.

Lebedev, who owns British newspapers such as the Independent and the Evening Standard, said he was battling rogue officers from the Federal Security Service (FSB), the main successor to the Soviet-era KGB, who were trying to take his assets.

After a raid on his bank by armed police last November, he said the officers were trying to take his assets, including a $200 million stake in Gazprom and 14.5 percent in Aeroflot. The FSB declined to comment.

But with an ironic smile, Lebedev said he would still like to join Putin's All-Russian People's Front, created in April to widen support for his ruling United Russia party.

"There is one boss and I am trying to join his front, with conditions by the way," Lebedev said with a chuckle.

"Nobody knows what the front is about, what are they fighting for -- is it just to love Putin or what? Putin is a gift of God, I heard," said Lebedev. He said he was not teasing Putin: "I am smaller than a mosquito."

Putin's spokesman Lebedev was welcome to join.

When asked if he will run for president, he pauses: "It is impossible: they could never allow that." One day? "Yes maybe."