* Ruling party seen winning despite ratings slump

* A test for Putin's power across 11 time zones

* At stake is United Russia's super majority

* Critic Navalny cries foul, pushes tactical voting

By Tom Balmforth

MOSCOW, Sept 17 (Reuters) - Russia goes to the polls on Friday to elect a new parliament in a three-day vote that the ruling United Russia party is expected to win despite a ratings slump after the biggest crackdown on the Kremlin's critics in years.

The vote is a test of President Vladimir Putin's grip on power across 11 time zones from the Pacific Ocean to the Baltic Sea as the Kremlin faces malaise at home over faltering living standards and dire ties with the West.

At stake is United Russia's super majority in the 450-seat State Duma, which last year helped Putin ease through constitutional reforms that allow him to run for office again and potentially stay in power until 2036.

The vote runs until late Sunday and is seen as a dry-run for the presidential election in 2024, a highly sensitive moment for the Kremlin should it choose to embark on a political transition to a new figurehead.

Putin, a former KGB officer who turns 69 next month, has not said if he will seek re-election when his current term ends in 2024. He has served as president or prime minister since 1999.

The Kremlin leader's fiercest domestic critic, jailed anti-corruption firebrand Alexei Navalny, hopes a tactical voting campaign led by his team in exile can upstage United Russia and hurt its bid to secure a hefty new majority.

The 45-year-old ex-lawyer whose movement was banned as extremist this summer was jailed in March in a case he called trumped up after recovering from a poisoning with a Soviet-style nerve agent.

His allies, who accuse the Kremlin of a sweeping crackdown, have no chance of gaining even a toehold in real politics after they were barred from running for office because of their association with Navalny's network.

The Kremlin denies any politically-driven crackdown and says individuals are prosecuted for breaking the law.

UNDER PRESSURE

The Communist party led by 77-year-old parliament veteran Gennady Zyuganov is seen as the ruling party's strongest rival at the vote, followed by the LDPR party headed by 75-year-old nationalist Vladimir Zhirinovsky.

Both those parties, like the Just Russia party, back Putin on many key policy matters.

Navalny's allies call the election a sham and have told supporters to vote for candidates they think have the best chance of defeating United Russia in their respective districts. Many of those politicians are communists.