* Ruling puts pressure on two sides for an agreement
* Fiat "looks forward" to resolving dispute in court
MILAN, July 31 (Reuters) - Fiat may step up efforts to negotiate a full buyout of majority-owned Chrysler out of court, sources said, after a Delaware judge prolonged the Italian carmaker's legal tussle with a minority shareholder, the UAW union healthcare trust.
Fiat said it "looked forward" to solving a dispute with the trust in court after winning a partial victory on Tuesday in its bid to buy the 41.5 percent of Chrysler it does not own from VEBA, the United Autoworkers-affiliated healthcare trust.
Delaware Chancery Court Judge Donald Parsons accepted the carmaker's legal positions in two pivotal disputes with VEBA. But he stopped short of ordering VEBA to sell 54,154 Chrysler shares to Fiat for $139.7 million, as the latter had sought, saying certain questions still needed to be answered through testimony at a trial.
The ruling will trim an estimated $500 million from the price tag for Fiat to buy out the VEBA trust, investment bank UBS said on Wednesday, cutting its estimate of the value of VEBA's 41.5 percent stake to $4.0 billion from $4.5 billion.
"We view the ruling as positive for Fiat and likely to help an out-of-court agreement," said UBS analyst Philippe Houchois in a research note. "We still view end 2013 as a likely deadline for an agreement as VEBA."
The ruling forces the two parties to step up talks if they want to come to a deal quickly, people familiar with the matter said. But the lower price Fiat is likely to pay for the disputed part of the stake may make VEBA a tougher bargaining partner, one of them noted.
The UAW became Chrysler's second-largest shareholder when Chrysler emerged from bankruptcy in 2009 and the union swapped future healthcare payments owed to it for a stake. The VEBA trust manages those healthcare benefits on behalf of the union.
Fiat runs the two automakers as a single company, but wants to buy the rest of Chrysler to squeeze out more synergies, cut borrowing costs and access some of Chrysler's cash flow.
While the price tag for Fiat may now fall, the timeline for the deal remains blurred.
"Fiat looks forward to resolving the few remaining issues in the litigation, through the discovery requested by the judge, and remains confident that those residual issues will also be resolved in its favour," Fiat said in a statement on Wednesday.
Any trial is likely to take between a year and 18 months, said a person familiar with the matter. But the judge's ruling offered Fiat no indication of when it would start.
Fiat's lawyers will now be forced to argue in court with representatives of the healthcare trust about why Fiat should pay less than the trust is asking in a deal the latter needs to pay future benefits for retired Chrysler workers.
Fiat shares were volatile, rising 0.25 percent to 6.05 euros at 1429 GMT.
"The ruling is a step forward and is good news," said a Milan trader. "But it's not decisive and the market is not discounting it as a done deal yet."