By Crispian Balmer
ROME (Reuters) - The Italian Senate voted on Tuesday to curtail its powers in a victory for Prime Minister Matteo Renzi, who has overcome determined opposition to push through the reform that he says will make the country more governable.
Renzi has attached considerable political capital to the bill, which looks to reduce the number of senators by two-thirds, strip the chamber of its ability to bring down a government and sharply limit its scope to block legislation.
Because it involves a change to the constitution, the reform will have to return to the Senate for another vote next year and will also have to pass twice through the lower house, giving its opponents ample opportunity to ambush the package.
It will then be put to a referendum, adding a further awkward hurdle to its eventual ratification.
However, Tuesday's vote came as a relief to the center-left government, which had faced attacks from both inside and outside its own ranks, with critics saying the overhaul will diminish Italy's democratic credentials.
Most opposition parties abandoned the 320-seat chamber ahead of the vote, which Renzi's coalition won by 178 to 17.
Drawn up after World War Two, the Italian constitution gave identical powers to both houses of parliament, boosting the checks and balances inside the political system in an effort to prevent the rise of another dictator like Benito Mussolini.
However, different electoral laws altered the make-up of the twin chambers. This made it hard for prime ministers to pin down secure majorities in the two houses and contributed to a stream of revolving-door governments over the past 60 years.
Renzi's reform will cut the number of senators to 100 from 320. Most of them will be drawn from regional councils and will no longer be directly elected. They will only have a full legislative say over proposed changes to the constitution.
The senate shake-up follows a stream of other government initiatives since Renzi took office in 2014, including a new electoral law, a reform of the education system and jobs market, and a major revamp of banking norms.
"The long season of inconclusive politics is over. The reforms are being done. Italy is changing," Renzi wrote on his Facebook page on Tuesday.
Renzi says his work has helped pull Italy out of recession, but critics say the changes will make little impact in a country where vested interests still hold considerable sway.
The government has a majority of less than 10 seats in the Senate, and a faction within Renzi's own Democratic Party (PD) party had expressed concern over the planned reform, making its passage through the chamber fraught with difficulty.
(Writing by Crispian Balmer; Editing by Steve Scherer)