By Brian Love and Emile Picy

PARIS (Reuters) - France's government, overriding street protests and rebels in its own ranks, invoked special powers on Tuesday to impose labor legislation by decree that will make it easier for employers to hire and fire staff.

President Francois Hollande's government hopes the labor reform will cut stubbornly high unemployment.

But less than a year from elections, the decision to ram through the contested reform without parliamentary support is a political gamble for the unpopular Hollande and a Socialist government targeted by mounting left-wing violence.

Thousands marched through Paris and other cities under heavy police presence in what labor unions say will be the last of a dozen such demonstrations before a summer holiday hiatus.

Turnout estimates varied - 45,000 according to the CGT union but no more than 7,500 according to police - but were in any case lower than in previous rallies.

Right-wingers walked out of the National Assembly and rebels in his own party watched, stone-faced, as Prime Minister Manuel Valls announced he would use constitutional powers to bypass the lower house of parliament during a second review of the reform.

"My government is determined to move forward, because the tactics of some ... cannot be allowed to block the country," Valls said in a swipe at Socialist rebels who refused to vote for the law.

At issue are reforms designed to cut a 10 percent jobless rate by making it easier to hire and fire. It would also allow firms tailor pay and work terms to company needs more easily.

"This is sad," said Laurent Baumel, one of 30 or more Socialists who contend the law betrays left-wing principles. "Valls seems to have refused out of customary intransigence."

The dissidents narrowly failed to muster enough sponsors in May to table a vote of no confidence in their government during the first reading of the labor reform. They were weighing options on Tuesday. A no-confidence bill is unlikely to pass.

"This move is an admission of failure," Philippe Martinez, the head of the hardline CGT union that has led the protests, said of the government's decision to bypass parliament.

Violence during months of street protests resulted in almost 2,000 arrests and left hundreds of riot police hurt in running battles with gangs of ultra-violent youths, many of them chanting anti-capitalist slogans.

That violence on the fringe of street marches has coalesced with other anti-government acts. Government spokesman Stephane Le Foll said on Tuesday 30 Socialist party buildings had been attacked in recent weeks, including one sprayed with gunfire.

(Editing by Ingrid Melander and Richard Balmforth)