* Lower house to vote on non-binding motion on Wednesday
* New jets will replace ageing fleet - defence minister
* PM Letta's PD party risks split in vote
By Paolo Biondi and Steve Scherer
ROME, June 25 Italy's cash-strapped government plans to go ahead with purchasing 90 Lockheed Martin F-35 fighter jets, Defence Minister Mario Mauro said on Tuesday, ahead of a vote that risks splitting the ruling coalition.
The lower house of parliament is due to vote on Wednesday on a motion, presented last month by opposition groups and some members of Prime Minister Enrico Letta's centre-left Democratic Party (PD), that calls on Italy to drop the fighter investment.
To avoid a split, the government may introduce a compromise motion calling for further study of the Lightning II Joint Strike Fighter (JSF) programme, but not its cancellation,
"We need to have the data at hand, collect the technical details, because its a very complex choice," said Graziano Delrio, minister of regional cohesion and a member of the PD.
The F-35 is a delicate issue for Letta's uneasy right-left coalition government, which is struggling to manage a huge public debt and limit its budget deficit to a forecast 2.9 percent of gross domestic product this year, a fraction below the European Union's 3 percent ceiling.
The PD said it wanted to cut spending on the programme before national elections earlier this year, but its coalition partner, the centre-right People of Freedom party (PDL), supports the purchase.
Mauro said the government had no plans to cancel its order. "They are 90 combat jets that will replace 256 obsolete aircraft that will be retired, and our newest fighter is now 30 years old," Mauro said in an interview with state television RAI.
Italy currently plans to spend 11.8 billion euros ($15.43 billion) on the jets over 45 years, starting in 2015, Mauro said.
The deal includes a provision to give maintenance contracts to state-controlled defence group Finmeccanica, as Italy's aerospace industry is a development and production partner in the F-35 project and Italy has already invested about 2 billion euros in it.
Last year, Italy cut its F-35 order to 90 warplanes from the 131 it had agreed to buy more than a decade ago, a move it said would save 5 billion euros as it sought to reduce defence spending to shore up its accounts during the economic slump.
With the country still in recession, the money saved by eliminating a single F-35 could be used to build 387 day care centres or renovate 258 schools, according to the motion signed by 158 lawmakers who want to scrap the deal.
But the MPs - from the opposition 5-Star Movement and Left Ecology Liberty (SEL), plus more than a dozen from the PD - would need twice that number to muster a parliamentary majority for their motion, which even then would be non-binding.
($1 = 0.7649 euros) (Editing by Mark Trevelyan)