By Kathy Finn

NEW ORLEANS (Reuters) - The two sons of former New Orleans Mayor Ray Nagin have appeared before a federal grand jury in connection with a probe of Nagin's business dealings in the aftermath of Hurricane Katrina, their lawyer said on Tuesday.

The appearance of Jeremy Nagin, 28, and Jarin Nagin, 26, came as federal prosecutors have been investigating the former mayor's dealings with city vendors and other businesses during his time in office, which encompassed the 2005 Hurricane Katrina disaster and its aftermath.

While mayor, Nagin founded a countertop installation company with his sons, and their company received contracts from local Home Depot stores during the repair and rebuilding that followed Katrina.

An attorney for the Nagin brothers said the pair had received subpoenas to provide testimony and documents to the grand jury, and that they did so on Friday. He said he did not believe the sons were under scrutiny.

"They have not been identified so far as I know as targets," attorney Clarence Roby Jr. told Reuters.

A source with direct knowledge of the probe said in February that Ray Nagin was under investigation by federal authorities. The two-term mayor left office in 2010.

In June, businessman Frank Fradella pleaded guilty to a federal charge of bribing a public official through payoffs of cash and other items.

Court documents filed in connection with the plea identified the recipient of the bribes as "Public Official A." When asked whether the unnamed official was Nagin, Fradella's lawyer, Randall Smith, told reporters, "If it walks like a duck and talks like a duck, it's probably a duck."

The court filings said the conspiracy involving Fradella and the public official stretched over a four-year period, during which Fradella "provided payoffs in various forms" to the official to secure city contracts for his home-improvement business.

The payments included a $50,000 check that the government said was funneled through a third party's bank account "in an effort to disguise the illegality of the payment."

Fradella also admitted to making monthly payments in excess of $10,000 to the official "after Public Official 'A' left office in May 2010." In addition, Fradella admitted to providing "numerous truck loads of free granite" to the official.

An attorney representing Nagin could not be reached for comment Tuesday.

(Editing by Corrie MacLaggan, Cynthia Johnston and Peter Cooney)