The District of Columbia's U.S. attorney, Jay B. Stephens, has asked a federal judge to lengthen the prison sentence of mystery pilot Thomas L. Root because Root allegedly committed a felony the week after he pleaded guilty to five other felony charges.

Root, a Washington communications lawyer until he was disbarred this year, is the pilot who said he blacked out while flying his Cessna 210 from National Airport to North Carolina on July 13, 1989, and wound up ditching into the Atlantic Ocean near the Bahamas. After being tailed by 19 military planes for four hours, Root was rescued with an unexplained gunshot wound.

Root is awaiting sentencing by Judge John Garrett Penn after pleading guilty in June to felony charges of counterfeiting, forgery and defrauding clients seeking FM radio station licenses from the Federal Communications Commission.

According to court records, Root could face a sentence of 27 months to 33 months in prison. But Stephens is asking Penn to extend the term up to 41 months, in part because of Root's alleged conduct while he is free and awaiting sentencing.

Stephens's request stems from Root's activities involving a client from Austin, Tex., who was competing with other applicants for a broadcast license in Elgin, Tex.

Against the client's instructions, Root withdrew from the competition for the license on June 12 -- the week after his guilty plea -- by allegedly forging his client's name on settlement papers and directing the $25,000 settlement to be paid to Root.

Root's attorney, Eugene M. Propper, contends that the Texas case is not related to the felony charges to which Root pleaded guilty and should not be considered by the judge when Root is sentenced.

Stephens said that Root's activities after pleading guilty are fair game.

"He had no free ticket to ride the highway of crime," Stephens said in the records.

Propper said, "It has never been Root's position that he is entitled to 'open season' on committing crimes after the execution of the plea agreement. He has not sought any such immunity."

Separately, the National Transportation Safety Board released a report last week on Root's flight. While the report did not reach conclusions about what happened, it cast strong doubts on Root's version that the gun he kept in the plane accidentally fired.

The agency could not find any medical evidence to explain Root's blackout. The safety board said the gun could not have fired without the trigger being squeezed, and that Root was probably shot before the plane ditched in the ocean.