By Alexei Anishchuk

NARYAN MAR, Russia (Reuters) - Dmitry Medvedev was met with whoops of excitement from a small crowd when he arrived to inspect a run-down apartment block in this depressed town in Russia's Arctic north.

"Are your flats heated?" the president asked muffled-up residents of Naryan Mar, where temperatures sit below freezing for much of the year and where new buildings are rare.

People in the block told him that their heating often went off during winter because of power cuts in the river port town, where some live still in ramshackle wooden structures.

Medvedev in turn protested to municipal officials, who duly said all tenants would be moved out of the apartments and into new homes next year and that all slums would be gone by 2016.

Such trips as this one last month to Naryan Mar are not the

glamorous part of Medvedev's work, but they have taken on a new significance since he and Prime Minister Vladimir Putin announced last month that they plan to swap jobs next year.

At risk of being a lame duck until next May, when Putin is expected to take over as president, Medvedev is rolling up his sleeves and throwing himself into preparations for a parliamentary election on December 4.

United Russia, led by Putin, is sure of winning the election. But the margin of victory is important because the party wants to keep its two-thirds majority in the lower house, which makes constitutional changes possible if needed.

The size of the victory will also reflect on Medvedev personally. His name is the first on the party's list of candidates, and a disappointing performance could affect the legitimacy of Putin's plan to make him prime minister in May.

"If the party fails at the polls, I think it would be hard for Putin to comply with his part of the deal," said Gleb Pavlovsky, head of the Foundation for Effective Politics think-tank and a former Kremlin spin-doctor.

HIGH STAKES

The stakes are high for Medvedev, whom Putin annointed in the Kremlin in 2008 after he himself had served the legal limit of two consecutive terms. The 46-year-old protege has kept the presidential seat warm until Putin can be re-elected next year and now has much to prove to voters after failing to carry out many of his promises as president or emerge from Putin's shadow.

In Naryan Mar, the welcome was polite but skeptical: "I live in an old building and I don't think he could change that," said one woman who would give her name only as Natalya. "But there's not much going on here, so we are happy he's come anyway."

Medvedev has been a frequent traveler but now his trips look increasingly like a dress rehearsal for his future role, and reveal he has some way to go to perfect his performance:

"Will I vote in the elections? No way. I don't trust politicians," said Viktoria, who works at a power plant in Krasnodar to which Medvedev also paid a visit this month and where he also promised investment in local infrastructure, as well as chiding United Russia activists to campaign harder.

The tough talk - including a televised spat with ambitious finance minister Alexei Kudrin, who then quit - as well as the crowd-pleasing promises differ are familiar tactics of a Kremlin that these days fights real elections but intends never to lose.

"Medvedev is using Putin's tested pre-election tricks as he has little time left to come up with something new to bolster United Russia's ratings," said Yevgeny Minchenko, director of the International Institute of Political Analysis.

POLLS SLIPPING

Buoyed by oil exports, support for United Russia is enough to guarantee victory, so Medvedev's real test is to retain two thirds of State Duma seats house and so virtually total control. But the job swap deal and other grumbles seem to be eating in to the party's ratings[nL5E7KQ0MG]. One poll this week showed it on 41 percent of voting intentions, off from 50 percent in January.

Pavlovsky said Medvedev needed to carve out his own image and differentiate himself from the man who now seems set to rule Russia until 2024 if he is to pull voters back to United Russia.

"Putin, who is now a strong prime minister himself, will soon have a weak prime minister in Medvedev who is unable to make independent decisions," said analyst Dmitry Oreshkin.

Medvedev has promised to overhaul the government to counter fears of political and economic stagnation once Putin is sworn in as president, a few weeks after the presidential election he is all but certain to win in March.

But he risks becoming a scapegoat, either if United Russia does not do well enough in the December election or if public dissatisfaction grows next year over the state of the economy.

"Putin could sack Medvedev at any moment if the overall situation in the country deteriorates seriously and he needs to replace him with a strong leader he can rely on," Oreshkin said.

The economy, vulnerable to fluctuations in global energy prices, suffered from its customers' economic crisis in 2008-09 but used funds it had saved for a rainy day to get through.

It has bounced back but foreign investors are still wary, and the rouble and stocks have been under pressure for weeks. Russian assets trade at big discounts to other emerging markets.

Some $50 billion dollars in capital has gone abroad over the past year and many say reforms are vital to maintain the pension system and reduce reliance on energy exports. [nL5E7KU0D6]

QUESTION OF LOYALTY?

Putin, a former KGB officer, has long been loyal to his allies. Many members of his government have served at the top level for a long time. He and Medvedev, whose background is as a lawyer, have been friends since they worked together in the St Petersburg city administration in the 1990s.

But as prime minister Medvedev will be vulnerable if another global economic downturn hits Russia, even though Putin says Moscow will be better prepared this time for any shocks.

Putin has shown ruthlessness in sacrificing Kudrin, another of his old Petersburg team. And some observers say he seems to have lost faith in his protege, despite assurances from their spokesmen that the pair get on well and see eye-to-eye on policy.

Commentator Yulia Latynina said: "The future prime minister Medvedev will answer for everything. And as soon as something goes wrong in the economy - well, there he is, Medvedev."

Last month a poll showed Medvedev holding an impressive 62 percent approval rating, just six points less than Putin's, yet impressions that he is dominated by the older man, particularly after the deal to switch roles, risk eroding that popularity.

Uncertainty is growing behind the Kremlin walls. Some of his officials had urged Medvedev to seek a second term as president. They now fret that he can no longer show much authority.

Consider his setpiece annual address on the state of the nation, a moment to set out achievements, and goals for the new year. "No one knows what he should be talking about this time," the Kremlin official said of drafting the year-end speech.

Already, even in foreign policy, a domain normally reserved for the president, it is unclear what role Medvedev can still play. It was Putin who just made a high-profile trip to China.

Medvedev will still take the stage to represent Russia at next month's G20 meeting in France and an Asia-Pacific Economic Cooperation (APEC) summit in Hawaii. But it is far from clear how much time Western leaders, who once saw in him an agreeable, more liberal alternative to Putin, will spare for the president.

In July, German Chancellor Angela Merkel playfully called him "Mr. Candidate," hinting at talk - apparently from Medvedev himself - that he might challenge for a second term. Now, as a soon-to-be "Mr. Ex-President," he may find fellow heads of state looking over his shoulder again for the familiar Vladimir Putin.

(Writing by Alexei Anishchuk and Timothy Heritage; Editing by Alastair Macdonald)