* Democratic Party leader eyes deal with Monti
* Leftist ally warns him not to risk election pact
* Berlusconi cuts into centre-left poll lead
ROME, Feb 6 (Reuters) - The leader of Italy's centre-left Democratic Party is facing pressure to ditch his leftist allies and seek a pact with outgoing premier Mario Monti as a resurgent Silvio Berlusconi threatens to spoil an election victory that once seemed assured.
With national elections due on Feb. 24-25, Berlusconi's mix of German-bashing rhetoric and promises to scrap the hated IMU housing tax is causing growing alarm on the centre-left, which has seen its impregnable-seeming opinion poll lead chipped away.
Democratic Party leader Pier Luigi Bersani has given increasingly explicit signals that he is interested in joining forces with Monti against Berlusconi, who has attacked both with equal vigour on his near-daily television and radio appearances.
"I've always said I want 51 percent but that I'd be ready to turn to other groups that are against Berlusconi and the Northern League if I had 49 percent and I'm very ready to turn to other groups including Monti's," he told RAI state radio.
On Wednesday, Berlusconi said his own internal polls showed his centre-right alliance with the pro-devolution Northern League party was just 2.4 percentage points behind the centre-left and he repeated he was confident of winning.
Most other polls make the difference greater, with a survey on Tuesday from the SWP institute seeing a gap of 5.6 points, but all agree the divide has narrowed since the start of the year.
So far, Bersani has rejected suggestions that he could abandon his coalition partner Nichi Vendola, the openly gay head of the small Left Ecology Freedom (SEL) party who has strongly opposed any deal with Monti's centrist group.
But Vendola himself has expressed growing concern that the senior partner in the centre-left coalition could be having second thoughts.
"I hope that Bersani does not want to take the responsibility of breaking the centre-left alliance," Vendola said in a tweet on Wednesday.
The PD responded with a statement from Francesco Boccia, a former rival of Vendola in regional elections, in which he called the alliance with SEL "essential to boost jobs and growth".
Barring an extraordinary surprise, Bersani is still the favourite to win the lower house and become prime minister but the race for the Senate, based on individual battles in each of the 20 regions, is more complicated.
To gain the upper house majority he would need to govern, he may have to rely on a deal with Monti, which could throw his existing alliance with Vendola into question.
Monti himself has fed the speculation, saying that he would not rule out serving as a minister in a reformist government led by another leader but repeating that he would not join an alliance that included Vendola.
"If Bersani is interested, as he has declared, then he has to make a choice within his own alliance," he told reporters at the margins of a conference.
For a deal to be struck, the two sides will have to overcome differences which have emerged ever more clearly as the campaign has gone on.
For the moment, Berlusconi's eye-catching promises to slash taxes, stand up to German Chancellor Angela Merkel and pull Italy out of recession have overshadowed their cautious campaign talk of economic reform and improving social equity.
Monti and Bersani have had a number of testy exchanges and the centre-left leader has been deeply annoyed by what he sees as Monti's lack of appreciation for the support given by the centre-left to his technocrat government.
For his part, Monti has been scathing about Bersani's allies on the left, principally the leftwing CGIL trade union and Vendola, who opposed his government and who has been harshly critical of the austerity policies it imposed.
Bersani has said he will stick to the path of economic reform and fiscal discipline laid out by Monti, while putting more emphasis on social justice and promoting economic growth but he has been short on specifics.
That at least has spared him from spelling out clearly where exactly he stands on issues such as labour reform, which Monti wants to toughen, or on pensions, where Vendola wants to roll back some of the reforms of Monti's technocrat government.
As the vote draws nearer, he will face increasing pressure to make a choice, say analysts.