Putin, who swapped his Kremlin post for the premiership in 2008 because of term limits, signaled last week that he may return to the presidency in 2012. Strong popular support and fawning state media would virtually guarantee him re-election.

A constitutional change, hastily agreed last year, would allow Putin two fresh six-year terms, so he could stay in power until 2024 when he would be almost 72.

That scenario alarms modernizers who remember ailing Soviet leaders like Leonid Brezhnev, who ruled from 1964 until his death in 1982 after several strokes.

"Brezhnev is not altogether a stupid analogy," said Igor Yurgens, who runs the Institute for Contemporary Development, a think-tank which advises Medvedev.

Asked at the Reuters Russia Summit whether Putin could become another Brezhnev, he replied: "Yes, why not? These risks exist ... the cult of personality is in our genes."

Yurgens said Putin's first eight years in the Kremlin had been "very good" for Russia and that his choice of Medvedev to succeed him as president indicated that so far he did not want to become a Brezhnev-type figure.

But the best way of avoiding such a scenario would be to encourage an "open, transparent competition between Putin and Medvedev" in 2012 as the leaders of two different factions in Russian government, he added.

Were Putin to run again and win in 2012, he would face an inevitable slide in his reputation, Yurgens added.

"I already feel among the people who drive me, who sell me groceries: 'OK, good prime minister, we'll support him'. But if he's there for another 12 years, believe me, this fatigue of the face and many other problems Russians associate with the top man will make his life emotionally miserable."

Yurgens, who is also the vice-president of the Russian business association, said there was a "clash of interests" in Russia at present between conservatives and statists on the one hand and liberals on the other.

"This confrontation was accelerated by the crisis," he said. "The conservatives and statists became more consolidated and probably more resourceful than the liberals and progressives. We will see a very real showdown."

Pressed on who he thought would win, Yurgens said he estimated the relative strength of conservatives and liberals as 70-30, both in the country at large and among the elite. Medvedev represented the liberal wing, he added.

Pro-Western political commentators and diplomats in Russia have criticized Medvedev for a lack of clear results from his reform program after nearly a year and a half in office.