Prime Minister Vladimir V. Putin, who transformed post-Soviet Russia by imposing Kremlin control over most aspects of public life, moved on Saturday to return to the presidency and could remain until 2024, giving him a rule comparable in length with that of Brezhnev or Stalin.
 

The move brings an end to years of uncertainty, inside and outside Russia, about whether Mr. Putin intended to loosen his grip on power. Neither leader offered any reason for the decision, but Mr. Putin said the deal had been made years ago. If that is true, Mr. Medvedev’s presidency, and the tension that accompanied its end, now looks like an orchestrated political drama that drew in much of the world.
 

Mr. Putin is by far the country’s most popular politician, and he is likely to face only token competition in the March election, given the complete marginalization of any opposition parties. One of Mr. Medvedev’s first acts as president was to extend the term to six years, meaning that Mr. Putin could serve for up to 12 years. If that carries through, he will have been Russia’s pre-eminent leader for more than 24 years, putting him in the same category as two of the Soviet Union’s definitive leaders: Leonid Brezhnev, in power for 18 years at the height of the cold war; and Josef Stalin, who kept a grip on power for roughly 30 years.

“The fact that the president, as a politician, betrayed those who believed in him — that is political self-annihilation, and he has the right to do it,” Mr. Pavlovsky told the radio station Ekho Moskvy. He called the move “a blow to the prestige of the institution of the presidency in Russia.”

Various political experts questioned Mr. Putin’s assertion that the decision was long since set in stone. The economist Mikhail G. Delyagin, a former government aide, said Mr. Medvedev had “exhibited a degree of independence,” and, if elected to a second term, could have tried “to become a real president and not a technical one.”

“I know that Putin and Medvedev had to clarify their agreement several times and that at times these conversations were difficult,” said Mr. Delyagin, director of the Institute of Globalization Issues. “There were moments where there was absolutely a sense that Medvedev spat on this agreement and tried to play his own game. But in the end he turned out to be weak.”