* Putin visits police academy in Siberia
* Says Moscow police will receive further pay rise
* Opposition rallies expected in Moscow, other cities (Adds detentions at Moscow protest)
By Gleb Bryanski
BARNAUL, Russia, Feb 21 (Reuters) - Russia's Vladimir Putin sought to bolster his authority ahead of a March presidential election on Tuesday by promising hefty pay rises for police in Moscow where opposition activists are gearing up for more protests demanding political change.
Putin, now prime minister, is all but certain to win a six-year term in the March 4 vote but a wave of demonstrations since December has prompted him to shore up support among crucial interest groups including his powerful security apparatus.
Visiting a police academy in the Altai region, his final stop in a five-day trip across Siberia, Putin, 59, singled out police in Moscow as due for salary increases.
"There are problems with police (pay rises) in some regions, including Moscow and the Russian north," he told an audience in Barnaul ranging from cadets and rank-and-file officers to Interior Ministry officials.
"They also had a pay rise, but not as big as elsewhere ... The size of the wage increase in these regions will reach the same level," he said, promising further hikes.
Putin, a KGB spy in Soviet times, hopes to avoid a runoff by winning at least half the vote in the election, and has courted high-tech workers, striving middle-class entrepreneurs and defence industry employees in separate cities during the trip.
Police form a crucial part of Putin's security machine which has kept a lid on the opposition movement during his 12-year rule, dispersing unsanctioned protests when ordered but laying off when restraint is in the Kremlin's interest.
Tens of thousands of people have turned out for opposition protests three times since a Dec. 4 parliamentary election, venting anger over suspected fraud in his party's favour and calling for a "Russia without Putin".
Police have been dispersing smaller protests held without official permission in the runup to the election.
On Tuesday, Moscow police said they detained about 10 people protesting outside the Central Election Commission headquarters, while Interfax news agency cited a protest leader as saying 26 were detained.
Protests have been held nationwide but those in Moscow have been by far the largest, reflecting discontent among middle-class Russians who want change and are dismayed by the prospect that he could potentially remain in the Kremlin until 2024.
Putin and his protege, President Dmitry Medvedev, have handled police gingerly, instituting reforms meant to curb corruption while dispelling perception of police as servants of the state and themselves rather than the people.
As part of the reform, police wages have doubled since the beginning of this year but in some regions, including Moscow and the surrounding province, local bonuses were abolished, resulting in smaller pay increases than expected.
Critics say the reform, one of the biggest initiatives of Medvedev's term, only scratched the surface by largely just changing the name of the institution from the Soviet-style "militia" to "police", but doing little to change the culture.
Putin appears to have been taken by surprise by the scale of the biggest opposition protests since he rose to power in 1999.
Moscow police dispersed a protest that drew several thousand people the day after the parliamentary vote, jailing several opposition leaders, but changed tactics and left protesters alone at subsequent protests that were much bigger.
In Barnaul, local authorities have denied groups permission to hold rallies. In a show of defiance with a humorous twist, protesters placed stuffed animals and Lego men carrying banners criticising Putin on a central square on Sunday.
But among academy students who also do police work and enjoyed the salary increase, the mood was staunchly pro-Putin.
Vladimir, a student in his 20s who guarded a polling station in the parliamentary election and will do so during the presidential vote, said his monthly salary rose to 28,000 roubles ($940) from about 12,000 roubles ($400) months ago.
"I think we need to maintain stability and complete the police reform," said Vladimir, a student in his 20s who said he could only be identified by his full name with the permission of the academy's chief. ($1 = 29.7575 Russian roubles) (Reporting by Gleb Bryanski; Editing by Steve Gutterman and Maria Golovnina)