Vladimir Putin's plan to return to the Kremlin increases the chances of a 'grave political crisis' in Russia and scuppers hopes of genuine economic reform, one of the architects of his first presidential economic programme said.

Mikhail Dmitriyev said Prime Minister Putin's planned job swap with President Dmitry Medvedev after a presidential election next March would cement an inflexible political system that leaves little room for a reform of the economy.

His comments highlight the fears of many free-market economists that Putin's return, announced at a party congress in September, increases the long-term risks of Arab Spring-style turmoil in the world's biggest energy producer.

The prospect of a grave political crisis has become more likely after what happened in September, Dmitriyev, a 50-year-old economist who heads the Centre for Strategic Research, told Reuters in an interview.

In this situation, it is hard to expect any purposeful efforts at institutional structural reform.

With German Gref, now chief executive of state bank Sberbank, Dmitriyev crafted Putin's economic programme in 2000. His institute provides research for the government.

Dmitriyev said Russia's economy was likely to grow at about 3 to 4 percent a year if prices of oil -- its main export - remained high.

A sharp and sustained fall in oil prices was unlikely but the dismissal of Finance Minister Alexei Kudrin in September after a public disagreement with Medvedev had increased the risks to Russian fiscal stability, he said.

Without Kudrin it is difficult to imagine a figure who could counter the wave of populism so the risks of budgetary irresponsibility and instability rise significantly, he said.

RUSSIAN TURMOIL

Dmitriyev said Russia's economy had the potential to grow 6 percent a year if the authorities introduced major reforms of regulation, infrastructure and property rights.

This would be a possible scenario if there was a political window for carrying out structural reforms. But no such window is in sight yet, he said.

The authorities would continue to tinker with what he said were ultimately unsustainable social policies for fear of undermining popular support.

Some investors fear Putin could be repeating the mistakes of European leaders now engulfed in the euro zone crisis by putting off much-needed reforms for fear of upsetting voters.

Putin, 59, helped steer Medvedev into the Kremlin in 2008 and became prime minister himself to get round a constitutional limit on two successive terms as president.

Putin remains Russia's most influential and popular leader, crafting an image of a macho leader who has brought economic and political stability after the chaos brought by the fall of the Soviet Union in 1991.

But the Kremlin is sensitive to Putin's popularity rating which an opinion poll released this week put at its lowest level in more than a decade.

Kremlin supporters dismiss concerns about instability, citing gold and foreign exchange reserves worth more than $500 billion (312 billion pounds) and sovereign debt of just 10 percent of gross domestic product as evidence of Russia's strength.

But Dmitriyev said discontent was rising.

If this trend is maintained, then the risk of conflictual political turmoil increases, he said. Although this is by far not the only likely scenario, the authorities understand that it is possible.

(Writing by Guy Faulconbridge and Alexei Kalmykov, Editing by Robert Woodward)