By Deepa Babington and Alberto Sisto

ROME (Reuters) - Silvio Berlusconi, tipped to become Italy's prime minister after April's vote, suggested an Italian rival bid to Air France-KLM's (AIRF.PA: Quote, Profile, Research) offer for Alitalia could emerge, sending the airline's shares soaring.

Political rivals dismissed it as election rhetoric, however, and the main financial partner for the purported rival bid by tiny Italian carrier Air One said it would be practically impossible to make an offer for Alitalia (AZPIa.MI: Quote, Profile, Research) now.

Berlusconi, Italy's third-richest man, said on Thursday that neither he himself nor his holding company had any interest in bidding for Alitalia, which loses more than a million euros a day and is just a few months away from running out of cash.

He said he had contacted businessmen, but did not identify them.

Italy's top retail bank Intesa Sanpaolo (ISP.MI: Quote, Profile, Research), which backed an earlier bid from Air One, said it was not working on any offer and that it would be "unimaginable" to make an offer without conducting due diligence. Air One had no comment.

Berlusconi told reporters that Intesa was still interested. "Has Intesa pulled out? No, no, no," Ansa news agency quoted him as saying. "From what I understand it is clear that they are asking for their own chance to do due diligence."

Ansa also reported that Berlusconi had had a rare telephone conversation with outgoing Prime Minister Romano Prodi, arguing the case for the consideration of a rival bid. Prodi was quoted as saying any bid must be "serious" and be made by March 31.

Italy's economy minister overseeing the sale said any interested bidder should make a formal offer now or risk derailing the long-sought deal with Air France-KLM.