The unexpectedly sharp drop in support for Vladimir Putin's party in parliamentary polls has exposed the first shift in public opinion against the Russian strongman's dominance, analysts said Monday.

Yet despite signs that social changes were slowly eroding his popularity, the premier still has ratings that would be the envy of European politicians and should still sweep presidential elections in March, they added.

Once back in the Kremlin, Putin will be ruling from a potentially vulnerable position for the first time and has the option of either clamping down on dissent more tightly or easing the door to change.

"The authorities may try to tighten the screws even further but will soon discover they are no longer in a position to do so," Yury Korgunyuk of the INDEM research institute said.

"And then they will try to manoeuvre, permitting things that were banned before."

After holding 315 seats in the outgoing chamber, Putin's United Russia party managed to win just 238 out of 450 seats on 49.5 percent support, the first time either the ex-KGB chief or his party lost votes while in power.

The elections were largely viewed as a litmus test of Putin's decision to stand for a third term in power under a job swap with Dmitry Medvedev, who failed to come out from his mentor's shadow while president for four years.

"People simply got terrified that this could all drag on for 12 more years," said Maria Lipman of the Carnegie Moscow Centre. Putin could stay in power to 2024 by serving two presidential terms which are now to last six years.

"People felt like fools -- everything was decided for them without even a pretence of them being asked," said Lipman.

Putin had already suffered an unprecedented show of discontent in the run-up to the vote when he was booed by fight fans when he entered the ring at a martial arts showdown in Moscow.

"Based on these results, we will be able to ensure the stable development of our country," Putin said tersely in a post-election speech at party headquarters that sounded anything but jubilant.

The last years have seen social changes in Russia that could discomfort the elite -- the emergence of a new and potentially critical middle class and explosion in criticism of the authorities on the Internet.

"The fall in popularity was not entirely unexpected. It is caused by popular dissatisfaction with corruption, illegality and abuse of power," said Lipman.

Analysts said Putin should still easily win his third term as president in March against a weak field, even if his popularity ratings are now lower than the stratospheric 80 percent levels recorded four years ago.

"Putin should win in the first round of the presidential elections," said Konstantin Simonov of the National Energy Security Foundation. "The party's candidate is always more popular than the party itself."

Yet some openly wondered whether Putin may now grow more sensitive to domestic criticism as he seeks to reform in order to survive.

"This should change the nature of the political debate," said Mikhail Remizov of the National Strategy Institute, while the Paris-based investment bank BNP Paribas said in a research note it expected "a more aggressive anti-corruption campaign in the coming months."

Putin's command of Russia follows in part from the loyalty of a tightly-knit group of former security officers from his native Saint Petersburg whom he has installed in key government and state business posts.

The first hints of the new softer approach emerged with a report that Boris Gryzlov -- the ruling party chairman who has been parliament speaker since 2003 and another of Putin's Saint Petersburg friends -- could step down.

"It is time to change the format of how (parliament) works -- we have to listen more to our opponents and less to ourselves," an unnamed United Party official told the Echo Moscow radio station.