A prominent Democratic party fund-raiser for Barack Obama and Hillary Rodham Clinton was arrested in Manhattan on Tuesday and accused of trying to defraud Citibank of a $74 million loan, the United States Attorney’s office said. The fund-raiser, Hassan Nemazee, 59, had been a national finance chairman for Mrs. Clinton’s presidential campaign before raising more than $500,000 for Mr. Obama’s campaign after the Democratic National Convention last August. F.B.I. investigators found that Mr. Nemazee, a Park Avenue financier and the chairman of Nemazee Capital Corporation, had lied about his assets, which he claimed were worth hundreds of millions of dollars, according to the complaint. In order to secure the loan, Mr. Nemazee submitted fraudulent documents about his holdings to Citibank, offering information for accounts that “never existed or had been closed years before,” Preet Bharara, the United States attorney for the Southern District of New York, said in a statement. Mr. Nemazee was due in court on Wednesday afternoon, where the charge of bank fraud was to be formally presented. The charge carries a maximum prison term of 30 years and a maximum fine of $1 million. Investigators said the fraud had been going on since December 2006. F.B.I. agents stopped Mr. Nemazee at Liberty Newark International Airport on Sunday, and interviewed him before he was able to board a flight to Rome. On Monday, Mr. Nemazee repaid the $74 million loan in full to Citibank, according to the U.S. Attorney. Investigators found that Mr. Nemazee had provided false names, addresses and telephone numbers of institutions that he said could vouch for his assets. Instead, those numbers directed callers back to a number “controlled by Nemazee,” Mr. Bharara said in the statement. Mr. Nemazee had been a Democratic fund-raiser since the early 1990s, when he raised money for the Clinton-Gore presidential campaign. His father was a shipping magnate who later became a diplomat for Iran in Washington, where Mr. Nemazee grew up. Mr. Nemazee had given more than $450,000 over the years, mostly to Democrats, and entertained President Bill Clinton, Vice President Al Gore and Senator John Kerry, among others, at his Park Avenue home. There were questions raised, about his financial dealings in 1998, when Mr. Nemazee was named by Mr. Clinton to be ambassador to Argentina. The Senate Foreign Relations Committee rejected his appointment after Forbes magazine published a scathing article about his business dealings and Republicans questioned his qualifications. Mr. Nemazee was charged in 2009 with orchestrating a scheme that defrauded banks of nearly $300 million. He pleaded guilty to four fraud counts and was ordered to forfeit his $17.75 million Park Avenue duplex; an estate in southern Italy; a blue Maserati; shares in a yacht and private airplane; and $93 million in cash and securities. He was sentenced to 12 years in prison, and released conditionally in 2019.