Vladimir Putin's ruling party clung to a much reduced majority in parliament on Monday after an election that showed growing weariness with the man who has dominated Russia for more than a decade and plans to return to the presidency next year.

Putin's United Russia 49.5 percent of the votes on Sunday, compared with 64 percent support four years ago, and enough to take up 238 of the 450 seats in the State Duma lower house, almost complete results and projections showed.

The party received nearly one-third fewer votes than in 2007 and fell far short of the 315 seats it secured in the last Duma election, making it the biggest electoral setback for Putin since he rose to power in 1999.

Opponents said even this outcome was inflated by fraud. The leader of the Communist Party, on target to increase its representation from 57 to 92 seats, said the election was the dirtiest since the collapse of the Soviet Union in 1991.

Although Putin is still likely to win a presidential election next March, Sunday's result could dent the authority of the man who has ruled for 12 years with a mixture of hardline security policies, political acumen and showmanship but who was booed and jeered after a martial arts bout last month.

Many Russians voted against the system and Putin is the head of that system, said Stanislav Kucher, a commentator with Kommersant FM radio station.

Putin has a very difficult choice. To survive politically he needs to reform but he can only reform if he gets rid of many vested interests in the ruling circle. To stay as he is means the opposite of political survival.

Although Putin is still likely to win a presidential election next March, his authority

Putin has cultivated a tough man image with stunts such as riding a horse bare chested, tracking tigers and flying a fighter plane. But the public appears to have wearied of the antics and his popularity, while still high, has fallen.

Many voters, fed up with widespread corruption, refer to United Russia as the party of swindlers and thieves and resent the huge gap between the rich and poor. Some fear Putin's return to the presidency may herald economic and political stagnation.

PUTIN SAYS OPTIMAL RESULT

Putin and Medvedev, who took up the presidency in 2008 when Putin was forced to step down after serving a maximum two consecutive terms, made a brief appearance at a subdued meeting at United Russia headquarters late on Sunday.

Medvedev said United Russia, which had previously held a two thirds majority allowing it to change the constitution without opposition support, was prepared to forge alliances on certain issues to secure backing for legislation.

This is an optimal result which reflects the real situation in the country, Putin, 59, said. Based on this result we can guarantee stable development of our country.

But there was little to cheer for the man who has dominated Russian politics since he became acting president when Boris Yeltsin quit at the end of 1999 and was elected head of state months later.

His path back to the presidency may now be a little more complicated, with signs growing that voters feel cheated by his decision to swap jobs with Medvedev next year and dismayed by the prospect of more than a decade more of one man at the helm.

COMMUNIST GAINS

The communists made big gains and official projections put the left-leaning Just Russia on 64 Duma seats, up from 38, and Vladimir Zhirinovsky's nationalist LDPR on 56, up from 40.

Russia has a new political reality even if they rewrite everything, said Sergei Obukhov, a Communist lawmaker.

Many of the votes were cast in protest against United Russia rather than in support of communist ideals because the Party is seen by some Russians as the only credible opposition force.

Opposition parties complained of election irregularities in several parts of a country spanning 9,000 km (5,600 miles) and a Western-financed electoral watchdog and two liberal media outlets said their sites had been shut down by hackers intent on silencing allegations of violations.

Police said 70 people were detained in the second city of St Petersburg and dozens were held in Moscow in a series of protests against alleged fraud.

Opposition parties say the election was unfair from the start because of authorities' support for United Russia with cash and television air time.

The country has never seen such a dirty election, said Communist Party leader Gennady Zyuganov, who dismissed the official results as theft on an especially grand scale.

Zyuganov said police had barred Communist monitors from several polling stations and some ended up in hospital with broken bones. He said some ballot boxes were stuffed before voting began.

Election monitors were due to comment on the voting later on Monday.

Putin has as yet no serious personal rivals as Russia's leader. He remains the ultimate arbiter between the clans which control the world's biggest energy producer.

The result is a blow also for Medvedev, who led United Russia into the election. His legitimacy as the next prime minister could now be in question.

(Writing by Steve Gutterman, Editign by Timothy Heritage)