Russian lawmakers moved to lengthen the presidential term from four to six years on Friday with a vote that opponents called a step toward Vladimir Putin's return to power.

The change means that the powerful prime minister could serve a total of 20 years as president if he returns to the position as many expect.

The office of Russian president "already has more power than the General Secretary (of the U.S.S.R.), the czar and the pharaoh together," Communist Party leader Gennady Zyuganov complained shortly before the State Duma voted 388-58 to approve the constitutional amendment. It faces two more votes in the Duma, or lower house of parliament, and appears certain to be enacted. The Communists were the only Duma faction to vote against it.

Political analysts and Kremlin foes predict that President Dmitry Medvedev could step down as early as next year, making his former patron acting president and triggering elections in which Putin would run and likely win.

Vladimir Ryzhkov, a liberal democratic critic of the Kremlin and former member of parliament, described the amendment as just the first step in Putin's choreographed return to the presidency.

"Absolutely, I believe that," Ryzhkov said. "There is a small group of people in the Kremlin who want power for life."

State Duma speaker Boris Gryzlov denied that Medvedev planned to leave office before his term ends in 2012.

"Everyone must work to the end of his term," he said, according to the state-owned Russian news agency RIA-Novosti.

Asked whether the longer term was intended to benefit Putin in an interview broadcast on state television earlier this week, Medvedev avoided the question.

"I can say only one thing for sure, and that is that the new terms will benefit only whoever is elected to the office of President once the necessary amendments have entered into force," Medvedev said.

The former chess champion Garry Kasparov called the proposed change "a cynical message to the Russian population and the rest of the world. This regime — this clique — is saying, 'We are staying no matter what."'

Kasparov joined about 100 opposition activists at a Moscow demonstration. They chanted and held banners with slogans such as "Hands off the Constitution!" and "Enough lies, enough blood, enough Putin!"

Putin stepped down as president in May after serving two four-year terms. He was succeeded by Medvedev, a lawyer and former aide.

In the run-up to the March presidential elections, Putin refused repeated calls to seek a constitutional amendment allowing him to run for a third consecutive term, saying the constitution was sacrosanct.

But Medvedev proposed extending the presidential term last week in his first state-of-the-nation address this month. Putin had earlier endorsed the same idea.

Supporters say the change will bring Russia in line with other Western democracies that have presidential terms of similar length.

But the speed with which the proposal is sailing through parliament has left many wondering whether Putin's allies are already preparing for Medvedev's departure.

If Putin is planning an early return, he may find his path eased by the current financial crisis, some observers say.

Putin is widely credited with having rescued Russia from one crisis — the aftermath of Russia's default on its debts in 1998.

The legislation also requires approval by the upper house of parliament and by two-thirds of Russia's regional legislatures. The Kremlin-backed United Russia party — led by Putin — dominates all of Russia's legislatures.

Ultranationalist Vladimir Zhirinovsky said the measure would bring Russia "into conformity" with other nations, such as France, where the president is elected for five years.

But Zhirinovsky suggested other legislators were merely rubber-stamping the Kremlin's proposal.

"The only thing that makes me upset is that had the president offered to cut the term to three years, we would have applauded and voted the same way," he said.

Lawmakers also voted to extend Duma terms from four to five years.