An aspiring musician pleaded guilty yesterday to assaulting a federal air marshal on a USAirways flight from Philadelphia to Amsterdam in August and was subsequently sentenced to five years' probation.

U.S. Magistrate Timothy Rice also required Thomas Gorham, 39, of Marblehead, Mass., to perform 10 hours of community service per week during probation and undergo alcohol-abuse treatment.

The judge suggested that Gorham could perform the community service by playing his guitar at several nursing homes and a home for the handicapped in Marblehead.

Rice said if Gorham can demonstrate that after the first year of probation he has maintained employment and has stayed sober, he would vacate the requirement that Gorham perform 10 hours of community per week for the remaining four years of probation.

According to court papers, passengers were boarding the aircraft for an evening flight to Amsterdam on Aug. 17 when Gorham got into a tiff with flight attendants.

He had been asked to have his large acoustic-guitar case checked at the gate and placed in the aircraft's cargo hold.

Court papers said he grabbed the case from a flight attendant, threatened to "kill" her, spat on the lead flight attendant and began yelling obscenities.

Gorham admitted yesterday he was drunk at the time, embarrassed by the incident and had no intention of harming anyone.

"Really, I just can't drink again," he told Rice. "I have to be sober."

Two federal air marshals subsequently approached Gorham and identified themselves. Court documents said Gorham balled his fists and tried to strike one of the air marshals with his left hand.

Assistant U.S. Attorney Nancy Rue said Gorham had to be carried off the aircraft by marshals, and the flight was delayed for six hours.

Rice also ordered Gorham to write an apology to the air marshals, the flight attendants and USAirways.