Two accountants have been indicted on charges of tax evasion and helping hundreds of their clients file false city and state tax returns, resulting in the loss of millions of dollars. A 21-count indictment accuses Jeffrey C. Rosner, 52, of Queens, and David E. Cohen, 54, of Staten Island, of filing false returns for themselves and their wives from 1999 through 2003, District Attorney Robert Morgenthau said Tuesday. In those five years, Rosner and Cohen _ who had offices in the Empire State Building _ also helped at least 600 clients evade millions in taxes, charging up to $500 to prepare a tax return, the prosecutor said. “This is a massive tax fraud,” he said. “This case is one of the largest we’ve ever brought.”Mariani said investigators know the names of all the suspects’ clients. She and Stark suggested that people whose returns were prepared by the defendants contact the Finance Department or the district attorney before those offices contact them. Morgenthau said both defendants taught at local colleges – Rosner at Touro and Cohen at Rutgers and City College of New York. As for Rosner, Morgenthau said, from 1999 through 2003 he failed to report any of the $1.2 million he earned as a tax preparer, the interest income he charged on loans to clients or the rental income he received from three New York properties. In the same five years, Cohen underreported $500,000 in income from his accounting business, Morgenthau said…….Rosner’s lawyer, Richard Finkel, said, “Of course he’s going to plead not guilty. He’s a highly respected accountant. He will defend vehemently against the charges and in the end he will be vindicated.” Cohen’s lawyer, Joseph DeMatteo, did not immediately return calls for comment. Both defendants were expected to be arraigned later Tuesday.