A demonstration by at least 20,000 people on the eve of Vladimir Putin's inauguration as president turned into a battle with police Sunday after some protesters tried to split off from the approved venue and march to the Kremlin.

Club-wielding officers wearing helmets seized demonstrators and hauled them to police vehicles, dragging some by the hair, others by the neck. Several protesters were injured, including one man with blood dripping from his head down the left side of his face.

Three leaders of the opposition movement that gained new life over the winter were among those arrested: Sergei Udaltsov, Alexei Navalny and Boris Nemtsov.

More than 400 people were arrested, and Russia's chief investigative agency said it was considering filing criminal charges of inciting riots against some of them. Police reported that 12 riot police officers were injured.

Previous installments of an unprecedented wave of protests that burst out after fraud-plagued parliamentary elections in December had been marked by fastidious order. The crowds, sometimes as big as 100,000 or more, had carefully kept to agreed-upon meeting-places and routes, even making a point of thanking police who stood guard in vast numbers, but did not interfere.

Sunday's break in that pattern likely reflected a sense of anger and impotence among protesters upset that Putin was handily elected to a new term in the Kremlin despite their defiance. Putin, who imposed a political system that stifled dissent and who dismissed the protesters as callow, pampered youths and Western stooges, will be sworn in for a six-year term Monday.

Sunday's demonstration started out peacefully, with protesters cheerfully marching down a wide avenue to a square on an island near the Kremlin. Some were pushing baby carriages and carrying young children on their shoulders. Many held clever homemade posters.

Some demonstrators aimed to turn up the pressure by trying to split off and head to the Kremlin, on the other side of the river.

When a phalanx of riot police blocked their approach to the bridge leading to the Kremlin, the protesters formed human chains and chanted "This is our city" and "Putin is a thief." Some demonstrators hurled stones at the police, and throat-irritating gas wafted through the air.

After about an hour of tense confrontation, police began pushing protesters back toward the square and harshly detained some of them. Police then detained protesters who had remained peacefully on the square. Two of the opposition leaders were dragged away while addressing the crowd and the third before he could take the stage.

The ground was left littered with broken glass and splattered with blood. Putin's spokesman, Dmitry Peskov, defended the police action.

"I would have liked them to be tougher," he said on the Dozhd cable television channel.

Before the march turned violent, some of the demonstrators acknowledged that Putin's March election win was a blow to morale.

"It's true that some have been disappointed," said Yuri Baranov, a 46-year-old information technology specialist. But "the most important thing is that people have awakened."

Others admitted some doubts about whether the protests would spur any long-term change.

"I would like to think that our voice will be heard, but I am not totally sure of this," said Yelena Karpova, 47, who came to the rally from Tula, about 120 miles south of Moscow.

The opposition's effectiveness is weakened by its own amorphousness — it is a loose alliance of leftists, Western-oriented liberals, nationalists and other factions. Some demonstrators were clearly impatient with the lack of a clear and focused program.

"Create a party, or I'm going to the dacha," read a poster held by one demonstrator, referring to the summer houses to which Muscovites love to flee.