Medvedev's final endorsement of the legislation follows its quick approval by the Kremlin-controlled parliament and all of Russia's 83 provincial legislatures. If enacted, the change would not apply to Medvedev's current term, due to end in 2012.

Putin, who remains very popular, was barred constitutionally from seeking a third straight term as president. He tapped his longtime protege Medvedev as his favored successor, ensuring Medvedev's landslide election in March.

Putin then became prime minister and leader of the United Russia party, which dominates the Duma, and he is still seen as the man calling the shots in Russia. Putin has said the change was not tailored for him and would boost democracy. But the push to amend the constitution just months after Medvedev's election has led to speculation that his term could be cut short to allow Putin to return to the Kremlin.

Putin is not barred from running again after a break, and Medvedev's move to extend the presidential term sparked speculation that Putin might not wait until scheduled elections in 2012 to seek a return to the office.

Some analysts say Putin will need to act quickly if he wants to regain office because his popularity could be quickly eroded by the financial crisis.