A former D.C. police officer was sentenced to 23 to 69 years in prison yesterday in connection with two robberies of a Sears, Roebuck and Co. store in upper Northwest last year.

D.C. Superior Court Judge Robert Shuker told James T. Brown, a one-year member of the police force at the time of the robberies, that he had imposed a stiffer prison sentence on Brown than his three codefendants because Brown provided the gun and police badge used during the robberies.

Brown was convicted by a jury in June of masterminding robberies of the Sears store on Nov. 18 and 29.

During the second robbery, a fifth man, later killed in a chase with police, entered the store wearing Brown's police cap and badge and identified himself and the others as police officers who were responding to rumors about a pending robbery.

When the men were asked for further identification the man pulled out Brown's police revolver.

The longest sentence previously imposed on one of the codefendants was 15 to 45 years in prison.

Since his arrest, Brown has been assaulted twice at the D.C. Jail and his lawyer yesterday had asked Shuker to consider his vulnerability as a former police officer in imposing a sentence.