President Vladimir Putin said Monday that he would accept the post of prime minister if Dmitry Medvedev becomes president, and he promised not to divert any presidential authority to the prime minister's office.

Putin spoke at a United Russia congress that almost unanimously elected Medvedev as the party's candidate for the presidential election. In a rare show of disunity in the pro-Putin party, a single delegate opposed Medvedev in the 478-1 vote. The identity of the dissenter was unknown because the vote was by secret ballot.

"If Russian citizens express their confidence in Dmitry Medvedev and elect him president of the country, then I will be ready to head the government," Putin told United Russia delegates gathered for the congress at a hall in the Gostiny Dvor shopping center, near the Kremlin.

Putin waited a full six days to reply to Medvedev's offer to appoint him as prime minister. Medvedev made the offer last Tuesday, a day after Putin backed him as the next president.

On Monday, Putin again praised Medvedev, a first deputy prime minister and Gazprom chairman, as an apt administrator and urged voters to elect him as president.

"We should not be ashamed or afraid of transferring key powers of the country, the destiny of Russia, into the hands of such a man," Putin said from the podium.

Opinion polls consistently show that about 40 percent of Russians are ready to vote for anyone backed by Putin. Given that Medvedev has long led an informal race to succeed Putin, the president's blessing appears to have effectively handed him victory in the March 2 election.

Putin, 55, said he would not change the balance of power between the president and prime minister. Under the Constitution, the powers are strongly tilted to favor the president.

Medvedev, 42, sat stone-faced in the first row as Putin spoke about him. The two had entered the hall together, walking side by side past some 3,000 party officials and journalists.

Medvedev, who took the floor after Putin, pledged to continue Putin's policies, saying they would advance Russia on the international stage.

By agreeing to become prime minister in a Medvedev administration, Putin appears to have found a way to delay a decision on whether to keep power in his own hands or pass it over, political analysts said. Putin's second and constitutionally last consecutive term ends in May. Until last week, he had kept tight-lipped about the identity of his preferred successor and his post-presidency plans.

"By becoming prime minister under Medvedev, Putin would secure for himself the role of his guardian during the transition period, protecting Medvedev from the political risks that might be posed by rival Kremlin groups, such as the siloviki," said Tatyana Stanovaya, an analyst with the Center for Political Technologies. The siloviki are a loose grouping of hawkish security and military officials in Putin's administration.

Medvedev, a lawyer with a strong academic background, has no history in the security services and is seen as the most liberal of the possible successors preferred by Putin.

If Putin sees that Medvedev matures as a president, he will likely gradually transfer more power over to him, Stanovaya said. "If Medvedev fails, Putin could easily come back as the president," she said.

If the president resigns, the prime minister becomes acting president and organizes early elections, in which Putin could legally run. Putin served as prime minister under Boris Yeltsin in 1999, a post he held for six months until Yeltsin resigned and handed him the presidency.

Given a Russian tradition of blaming the Cabinet, not the president, for social problems, Putin's choice of Medvedev indicates that he feels comfortable with the younger ally, said Dmitry Badovsky, an analyst with the Institute for Social Systems. Putin and Medvedev have a father-son relationship, say people who know them personally.

Chechen President Ramzan Kadyrov, who attended the congress, told journalists that "99.9 percent of North Caucasus residents will support Dmitry Medvedev for the post of the president and Vladimir Putin for the post of Russia's prime minister." Chechnya reported a jaw-dropping turnout of 99.5 percent in the Duma elections on Dec. 2 -- the highest of any region. It said 99.36 percent of the voters chose United Russia.

Across town, Rosneft president Sergei Bogdanchikov said Putin becoming prime minister under Medvedev would "bring stability, plus a need for the rule of law."

"This is good and is a guarantee for business," Bogdanchikov said on the sidelines of a Rosneft reception Monday evening.

When asked whether he would consider taking up a post in the government, Bogdanchikov said: "I haven't been asked, and I haven't thought about it. I'm happy where I am."

In addition to United Russia, Medvedev's presidential bid has been supported by A Just Russia, a pro-Putin party that won State Duma seats in the recent elections, and two parties that did not win seats, Civil Force and the Agrarian Party. Medvedev is not a member of any party.

Vedomosti, citing an unidentified United Russia official, reported Monday that Kremlin chief of staff Sergei Sobyanin would serve as Medvedev's campaign manager. The Kremlin's press service would not confirm the report.

Also at the United Russia congress, delegates unanimously voted to confirm Boris Gryzlov as speaker in the next Duma and leader of the party's Duma faction. Gryzlov held both posts in the previous Duma. Deputies meet for their first session on Jan. 24.

United Russia won 315 of 450 seats in the Duma. Putin said at a United Russia congress on Oct. 1 that he would consider becoming prime minister if United Russia won a landslide victory and if it chose a "worthy" person to become the next president.

Staff Writer Miriam Elder contributed to this report.