* Scandal could damage Berlusconi's party
* Final polls show Berlusconi party trailing
MILAN, Feb 12 (Reuters) - Italian prosecutors accused the former governor of Lombardy, a once-powerful ally of Silvio Berlusconi, of criminal conspiracy after they completed a corruption investigation on Tuesday, less than two weeks before a national election.
The scandal could damage Berlusconi's People of Liberty (PDL) party in a powerful swing region, one of the most important battlegrounds in the race for the February 24-25 election.
A statement from the Milan prosecutors office said Roberto Formigoni, who resigned as governor in October, was accused of conspiracy as part of the investigation into the Salvatore Maugeri Foundation, a local health care group.
Final polls published on Friday before a two-week blackout ahead of the vote showed the PDL trailing the centre-left nationally by 5.7 percentage points.
But separate local polls on Lombardy and other key regions that determine the make-up of the Senate were too close to give a clear idea who might win the upper house.
Formigoni, who led the wealthy Lombardy region for 17 years, has been under investigation for some time for pocketing 8.5 million euros ($11.44 million) in presents, trips and dinners in exchange for favours.
He was not immediately available for comment but has repeatedly denied any wrongdoing.
Sixteen others are targeted in the same investigation. According to Italian law, a criminal inquiry must be formally closed before charges can be filed.
Lombardy, home of the financial capital Milan, will be a crucial battleground region in the national election, which coincides with a separate poll for a new regional government.
Centre-right parties have long dominated the region but a series of damaging corruption cases has weakened their support, leaving the result of the vote open.
Because of the complexities of the electoral law, winning the state, which has more Senate seats than any other, may be tantamount to gaining control of the upper house and forming a stable government.
($1 = 0.7427 euros) (Reporting by Giancarlo Navach; Writing by Steve Scherer; Editing by Michael Roddy)