Italy's mainly right-wing bloc is on track to win a broad majority in both houses of parliament at next month's national election, a study showed on Tuesday, benefiting from divisions among its opponents.

The conservative alliance leads opinion polls ahead of the Sept. 25 ballot, with the rightist Brothers of Italy set to be the largest single party. Italy's election law favours parties that form broad alliances.

On the basis of its election promises of tax cuts and higher pensions, a win by the conservative alliance may strain Italy's public finances, while the bloc would also be expected to crack down on illegal immigration.

The study by the Cattaneo Institute think tank, based on the latest polls, suggests the alliance could elect 245 lawmakers out of 400 at the Chamber, and 127 out of 200 at the Senate.

The conservative bloc includes Giorgia Meloni's far right Brothers of Italy, Matteo Salvini's right-wing League, Silvio Berlusconi's conservative Forza Italia and several minor centrist allies.

The centre-left led by Enrico Letta's Democratic Party (PD)would elect 107 lawmakers in the lower chamber and 51 in the Senate, while the rest of the seats would be divided among parties outside these main blocs, the study found.

Centrist and leftist parties have been struggling to join forces since the election was called last month following the collapse of Mario Draghi's broad "national unity" government.

The latest blow came on Sunday when the centrist Azione party quit an alliance of the PD and small centrist and leftist groups, citing the presence of parties who failed to support Draghi as one of the reasons.

Azione leader Carlo Calenda is now in talks to strike a deal with fellow centrist party Italia Viva led by former prime minister Matteo Renzi.

However, this alliance would get just 23 seats altogether in the two houses of parliament and the deal would boost the overall majority of the conservatives, the Cattaneo Institute study found.

"Unless in the coming weeks it turns out that (Azione and Italia Viva) are able to attract a very significant amount of voters from the centre-right, that would be the effect," Salvatore Vassallo, who heads the think tank, told Reuters.

The 5-Star Movement - which will almost certainly run alone - would get 27 seats in the Chamber and 12 in the Senate, according to the study.

The only consolation for the opponents of the conservative bloc, it found, is that it is "highly unlikely" to get the two-thirds majority it would need to impose constitutional reforms without the need for a referendum.

One such constitutional change - the direct election of the president - is a top priority of Brothers of Italy, whose leader Meloni is in pole position to become prime minister in the event of a conservative victory.

(Editing by Mark Heinrich)