Representative Michael G. Grimm, a former F.B.I. agent and Marine who capitalized on his straight-arrow image to win a seat in Congress, was expected to be indicted on federal fraud charges after a lengthy corruption investigation, people with knowledge of the case said on Friday.

The charges against Mr. Grimm, 44, a Republican who was first elected in 2010 and represents Staten Island and part of Brooklyn, were expected to include mail fraud and wire fraud, and to focus largely on his conduct in connection with a health food restaurant he owned on the Upper East Side of Manhattan after he left the Federal Bureau of Investigation in 2006, two of the people said. He was also expected to be charged with obstruction of justice, for allegedly lying under oath in a federal lawsuit.

The investigation of the second-term congressman, by the F.B.I. and the United States attorney’s office in Brooklyn, began more than two years ago with an examination of Mr. Grimm’s fund-raising for his 2010 race and expanded. Two of his fund-raisers have already been charged. One, Diana Durand of Houston, was charged with illegally funneling more than $10,000 into his campaign. The other, Ofer Biton, pleaded guilty to visa fraud charges.

But on Friday, it did not appear that the indictment would include any campaign finance charges or accusations that the congressman had misused his office, although several of the people noted that the investigation was continuing. They all spoke on the condition of anonymity as the charges had not been formally announced and they were not authorized to discuss the case.