BOSTON -- George Grasso, a former account manager with Roberts & Associates, a Natick, Mass.-based food broker, pleaded guilty last week to a single count of mail fraud in U.S. District Court here. Sentencing is scheduled for March 4. He faces a maximum sentence of five years in prison and a fine of up to $250,000. William P. Stimson, head of the Economic Crimes Unit of the U.S. Attorney's office here, said last week that, had Grasso's case gone to trial, his office was prepared to show that between 1988 and 1992 Grasso and others diverted for themselves a total of $127,000 in manufacturer promotional funds intended for retailers. Stimson said Grasso's role was to create documents that overstated the amounts due to particular retailers. Grasso couldn't be reached for comment.