Michele Sindona, the indicted Italian financier who played a key role in the largest bank failure in U.S. history, surfaced today as mysteriously as he disappeared more than two months ago.

It remained unclear whether Sindona had been kidnaped or had staged his disappearance. He vanished Aug. 2, slightly more than a month before he was to go on trial for fraud in connection with the 1974 collapse of the Franklin National Bank, which he controlled.

His family has insisted Sindona was snatched off Fifth Avenue by Italian leftists. Law enforcement authorities, including the U.S. attorney's office scheduled to prosecute him, simply listed him as missing.

Sindona was resting with a wound in his left leg at Doctor's Hospital tonight. FBI spokesman Quentin Ertel said Sindona, a former financial adviser to the Vatican whose personal fortune was once estimated at $500 million, had been sedated and agents would not be able to interview him until Wednesday.

Dr. Elliott Howard, who examined Sindona, said his leg wound could be the entrance and exit holes of a bullet. Sindona told Howard the wound was about three weeks old, United Press International reported. Howard said it is healing well.

A family statement said Sindona also is suffering from exhaustion.

U.S. marshals are guarding Sindona's hospital room. He is in stable condition, a hospital spokesman said.

The family's statement said Sindona was released "by his kidnapers at about 11:10 a.m. at Tenth Avenue and 42nd Street. He was picked up by his son-in-law and after examination by a doctor was admitted to Doctor's Hospital."

Sindona entered the hospital about 2:30 p.m., according to hospital spokesman John Donaher. He walked into the hospital without assistance.

Before the family issued its statement through the office of Sindona's lawyer, Marvin Frankel, FBI spokesman Ertel said that two of Frankel's associates had gone to Tenth Avenue and 42nd Street to pick up the financier and had taken him to the home of his son-in-law, Pier Sandro Mangoni.

Sindona disappeared while taking a walk near the Pierre Hotel, where he lived in a cooperative apartment. His family later received a message: "We now have Michele Sindona as our prisoner. You will be hearing from us."

A number of communications to the family and Sindona's lawyers in Italy followed, but none demanded ransom.

They included a letter in Sindona's handwriting and a photograph mailed from Brooklyn that showed him looking haggard. A group calling itself the "Proletarian Committee of Subversion For Better Justice" claimed responsibility for the kidnapping, according to Sindona's family. The communications threatened Sindona with "proletarian justice."

He had been free on a $3 million bond, which he made with $150,000 in cash and his apartment as collateral, awaiting the start of his trial Sept. 10. Under his bail provisions he had not been permitted to go anywhere except Long Island, New Jersey, Manhattan, the Bronx and several suburban New York counties.

Sindona was born in Sicily, where his father was a farmer.He began his financial climb by acquiring one of the few trucks available in Sicily in 1943 and transporting produce.

After the war Sindona went to Milan, where he became a friend of then Monsignor Giovanni Montini, who later became Pope Paul VI and often turned to Sindona for advice on Vatican investments.

While he was advising the pope, Sindona also came to know David M. Kennedy, then chairman of the Continental Illinois Bank and subsequently President Nixon's first treasury secretary.

Kennedy later became a witness for the prosecution in cases related to the Franklin National Bank failure.

The charges that Sindona misappropriated $45 million of that bank's funds are not his only legal problem.In Italy he is charged with illegally diverting $225 million out of the country to companies he controlled. At the time he disappeared, Sindona had been fighting extradition to Italy.