An Alexandria man was sentenced in federal court yesterday to life without parole for helping to hire a gunman who entered an Old Town housing project last year to collect a drug debt, then killed a police officer while trying to escape.

Armstead Gravette, 29, filed a last-minute motion through his attorney asking that his guilty plea be set aside because he is innocent, was "unduly influenced by his attorney" to plead guilty and did not understand the charges against him.

Gravette pleaded guilty in June to aiding a drug racketeering enterprise that led to the death of Cpl. Charles W. Hill and raised cries of outrage throughout the Washington region.

Assistant U.S. Attorney Liam O'Grady argued that Gravette knew the legal system intimately and pleaded guilty knowing the consequences. "This is a defendant who has appeared in court more times than I have as a prosecutor," O'Grady said.

Gravette has 17 misdemeanor and seven felony convictions, including assault, forgery and petty larceny.

Robert Stanley Powell, Gravette's attorney, told the court "there was no effort to try to coerce Mr. Gravette into this plea."

U.S. District Judge Claude M. Hilton, denying Gravette's motion, said his plea "was voluntarily entered" and there "is certainly a factual basis to support" the guilty plea.

Gravette is the third of four defendants sentenced in a case arising from a May 1989 incident in which a gunman carrying a sawed-off shotgun was sent to Eddie Jackson's Hopkins Court apartment to collect $3,700 Jackson owed for crack cocaine.

The gunman, Jamie Martin Wise, took four hostages, killed Cpl. Hill and wounded Officer Andrew Chelchowski before being slain by police officers as he tried to escape.

Jackson, 18, was sentenced to 20 years for his role in the drug conspiracy. Bruce Murrell, 19, of Brooklyn, N.Y., who hired Wise to intimidate Jackson, received a life sentence last week. Theodore Henderson III recently was arrested in the case and is scheduled for trial Sept. 25.

O'Grady condemned Gravette yesterday for introducing the gunman to Murrell and then planting himself in the Hopkins Court apartment during the hostage incident to make sure Wise did not steal Jackson's drug payment.

Gravette "watched as four people are robbed, their lives are threatened, one woman is raped," yet he did nothing to help them, O'Grady said.

Powell asked for some leniency because there was no intent on his client's part to help kill a police officer. However, Powell added, "I was a police officer myself for 10 years and every time I hear of the death of an officer, it brings tears to my eyes."

Sherry L. Davis, an Alexandria police officer and Chelchowski's fiance, wrote a letter to the court saying, "I have watched a good and dedicated police officer -- and the man I love -- suffer with severe physical pain every moment of every day since" the shooting.

"Tell those of us who have taken on the responsibility to care for the public welfare that those who choose to poison society with their drugs and destroy lives with their violence will not be tolerated."