(Adds details of findings, company background)

SAO PAULO, July 17 (Reuters) - Brazilian retailer Americanas SA is sharing with authorities new details of how it hid over $4 billion in debt, saddling investors with huge losses and doubts about what comes next for the 95-year-old brand, whose former executives are under police investigation.

The independent committee report on the accounting fraud, presented to the company's board and summarized for investors in a late Tuesday filing, adds to evidence that management cooked the books for years before a January 2023 bankruptcy filing.

The scheme involved improper entries in suppliers' accounts such as fictitious advertising budgets and financial operations incorrectly reflected on the company's balance sheet.

Americanas said in the filing that those responsible are no longer with the company and the internal report is being shared with federal police, prosecutors and securities regulators.

Last month, former chief executive Miguel Gutierrez was arrested in Madrid and later released as part of a police investigation. Brazilian authorities are pushing for extradition of Gutierrez, who has dual citizenship.

Another former executive targeted by the criminal probe, Anna Saicali, former head of e-commerce, recently returned from Portugal to Brazil and handed her passport over to police.

Attorneys representing Gutierrez and Saicali said in separate statements that their clients deny any wrongdoing and are collaborating with the investigation.

The scandal at Americanas, backed by three billionaires including Jorge Paulo Lemann, one of Brazil's richest men, sent shockwaves through financial markets and tarred a brand that has long been a fixture of Brazilian retail.

The company, based in Rio de Janeiro, is known for selling everything from chocolates to TV sets and women's underwear. But Americanas has struggled for years against fierce competition from more internet-savvy rivals such as Mercado Libre and Magazine Luiza.

"I am skeptical about the future of Americanas, about the sustainability of their business model," said consultant André Pimentel, a managing partner at Performa Partners who worked on a restructuring of Americanas in early 2000s.

The retailer was founded in 1929 in Niterói, across the bay from Rio's state capital, by a group including Austrian and American entrepreneurs.

Lemann and his partners, Marcel Telles and Carlos Alberto Sicupira, later acquired a dominant stake in the company. The three, who have not been cited in the police investigation, currently own around 30% of shares and have agreed to put up additional capital to rescue the distressed company. (Reporting by Luciana Magalhaes and Luana Maria Benedito; Editing by Brad Haynes, Kirsten Donovan)