SALEM – A Lynn man has admitted selling heroin to an undercover police officer during a city sweep of street level dealers in October 2009.Brian K. Gibson, 44, of 21 Whiting St., changed his plea to guilty Monday morning before Judge John T. Lu in Salem Superior Court to a charge of possession with the intent to distribute heroin.Sentencing is postponed for a week until Aug. 31.In the meantime, at the request of defense lawyer Christopher Norris, Gibson was allowed to remain free on his promise to return to court for the imposition of his punishment.Gibson, a former cook, is expected to receive two and a half years in the House of Corrections as part of a joint recommendation proposed to the court by Assistant District Attorney Kim M. Faitella and Norris.Faitella told Lu the charge arises out of a city-wide sweep by Lynn police.On the morning of Sept. 29 an undercover police officer approached Gibson at the corner of Lloyd and Washington streets asking him if he could get him a bag of heroin.Gibson made a phone call, left and came back with one bag of heroin for the undercover officer. The officer turned over to Gibson $60 in marked bills which were on his person when police moved in and arrested him.