(Adds mediator expects more talks, pro-government rally)
By Joan Magee and Daniel Bases
NEW YORK, Aug 12 (Reuters) - International banks are struggling to reach a deal to buy a chunk of Argentine sovereign debt held by New York hedge funds suing the country, dampening market hopes for a swift end to the country's latest debt default.
Citigroup, Deutsche Bank, HSBC and JP Morgan offered the holdout hedge funds 40 cents on the dollar for the roughly $1.66 billion of bonds, including interest, and raised the offer to 50 cents on Monday, sources told Thomson Reuters IFR.
Those negotiations are taking place parallel to faltering talks between Argentina and the holdouts led by Elliott Management Corp and Aurelius Capital Ltd.
Daniel Pollack, the U.S. court-appointed mediator overseeing the negotiations, told Reuters he expected more meetings with both sides, though he did not say when.
Monday's offer from the banks to the holdouts, who bought the bonds on the cheap during and after the country's 2001-2002 economic crash, remained far below the 80 cents first proposed last week.
"These are not fully-baked proposals," a source from one holdout firm told IFR.
Local Argentine bonds fell more than 1 percent on the day and the peso currency weakened on pessimism over a potential deal.
"Just when it looked like we might see a deal with the holders of the defaulted bonds, it vanished," said a research note from Buenos Aires brokerage Allaria Ledesma and Co.
The banks may be nervous about what reassurance they can obtain from Argentina that it will buy the debt back from them, and at what price.
"Our insecurity and the insecurity of the banks has been that the government hasn't given any indications regarding price points or structure once January hits," a source close to the talks said.
Argentina's latest debt crisis stems from its record $100 billion default in 2002. It restructured most of that debt in bond swaps that gave investors less than 30 cents on the dollar. But the holdouts went to court for full payment.
In 2012, a U.S. judge, Thomas Griesa, ruled Argentina could not repay holders of restructured debt without paying the hedge funds at the same time.
The government says it met its obligations to holders of exchanged debt when it deposited $539 million into the account of an intermediary bank for a June 30 coupon payment. But Griesa called the deposit illegal and blocked it.
The defiant stance of tough-talking President Cristina Fernandez against the funds she calls "vultures" has won growing support among Argentines, opinion polls show.
Several thousand government supporters beating drums and waving banners gathered in an entertainment hall in the Argentine capital on Tuesday, backing Fernandez's refusal to obey Griesa's order and pay the holdouts.
They filed past trash cans adorned with posters carrying the slogan "Fatherland versus Vultures" and showing the judge's face superimposed onto the scavengers. The Argentine government has accused Griesa of bias in favour of the funds.
"What country is in default if you've paid," said 59-year-old Juan Carlos Satta, echoing an oft-repeated government line that Argentina has honoured its debt payments. "Griesa is wrong." (Additional reporting by Davide Scigliuzzo of Thomson Reuters IFR in New York and Walter Bianchi and Richard Lough in Buenos Aires; Writing by Richard Lough; Editing by Steve Orlofsky and Lisa Shumaker)