* Fiat wants to buy UAW trust's 41.5 pct stake
* IPO may delay CEO's goal of merging Fiat, Chrysler
* JPMorgan is underwriter for IPO
By Deepa Seetharaman and Bernie Woodall
DETROIT, Sept 23 (Reuters) - Chrysler Group LLC was forced to file paperwork for an IPO by its second-biggest shareholder on Monday, escalating a spat with main owner Fiat SpA which said it could scale back its commitment to the U.S. automaker.
Fiat, which owns 58.5 percent of Chrysler, wants to take full control and buy out the rest of the stock owned by the United Auto Workers trust fund, but has balked at the more $5 billion being demanded.
In response, the UAW trust exercised a right enshrined in Chrysler's 2009 government-financed bankruptcy to go forward with an initial public offering, stepping up pressure on Sergio Marchionne, chief executive of both automakers, to reach a deal.
Bankers and analysts view the filing as a move by the UAW trust to extract a better offer from Fiat and many wager an IPO will never take place.
Fiat responded angrily in the filing, which raises critical questions about when and even if Marchionne can merge the two companies to form the world's seventh-largest auto group. The Fiat-Chrysler alliance was one of the centerpieces of the Obama administration's 2009 restructuring of the U.S. auto industry.
"Fiat has informed us that it is reconsidering the benefits and costs of further expanding its relationship with us," Chrysler said in its S-1 filing with the U.S. Securities and Exchange Commission.
Chrysler added that Fiat is also reconsidering the terms on which the Italian automaker will continue to share its technology, vehicle platforms, engineering expertise and other resources with Chrysler.
"Fiat is saying that Chrysler is worth less if we don't get that full integration," said Richard Hilgert, an analyst with investment research firm Morningstar. "It's a shot across the bow of the UAW."
The IPO, which for the purposes of calculating the regulator's registration fee was estimated at up to $100 million, will be underwritten by JPMorgan. Marchionne said in mid-September that if an IPO happens, it is likely to take place in the first quarter of 2014.
Chrysler did not say how many shares will be offered in the sale. The UAW trust fund intends to use the proceeds to pay for medical benefits for blue-collar Chrysler retirees.
Under Marchionne, Chrysler has mounted an unlikely comeback that has pushed its valuation to around $10 billion, according to some analyst estimates. The U.S. automaker is now propping up Fiat's bottom line, rather than the other way around.
Chrysler's success has complicated Marchionne's efforts to buy out the fund. The more than $5 billion price tag pushed for by adviser Brock Fiduciary represents the highest possible payout under the terms of the bankruptcy agreement.
Last week, Marchionne hired former U.S. auto task force leader Ron Bloom, chief architect of Chrysler's 2009 bankruptcy restructuring, to advise Fiat in its negotiations.
Bloom was instrumental in convincing the UAW to accept a stake in Chrysler as part of the bailout package. He also is advising Detroit retirees in the Detroit municipal bankruptcy.
Chrysler and Fiat currently are forced to manage their finances separately, even though they are run by the same executive team. A full merger would make it easier - but not automatic - to combine the cash pools of the two companies, giving Fiat more funds to expand its product lineup.
Chrysler, based in suburban Detroit, had cash and cash equivalents of $12.2 billion as of June 30. Its net profit in the first half of the year fell 21 percent to $764 million from $966 million in the previous year.
Chrysler remains heavily reliant on North America, which accounted for 90 percent of vehicle sales in the first half of 2013. It added that its lineup of smaller, less expensive cars are not as competitive as its larger, more profitable vehicles.
"Despite our recent financial results, we have not yet reached a level of sustained profitability for our U.S. operations," Chrysler said in the S-1 filing.
Monday's IPO filing reflects the unusual set of events that shaped the restructuring of the U.S. auto industry.
The UAW trust, a type known as a voluntary employee beneficiary association, or VEBA, was created in 2007 as a way for General Motors Co, Ford Motor Co and Chrysler to offload their obligation to pay retiree healthcare benefits.
The trust was initially supposed to be funded with cash. But as part of the 2009 financial crisis, it agreed to take stakes in GM and Chrysler in lieu of cash.
"The Chrysler IPO is a textbook example of the difficulties that can occur when debt is converted into an ownership stake, as it was during Chrysler's bankruptcy," said Jack Nerad, executive editorial director and market analyst of auto research firm Kelley Blue Book.
The IPO filing comes the same day GM bought back preferred shares held by the UAW trust for about $3.2 billion.
The trust is carved up into three separate accounts that pay for medical benefits for GM, Ford and Chrysler retirees. The trust is barred by law from using the assets of one account to defray costs of another.