Comcast Cable Communications Inc. is delivering on an earlier promise to deliver high-definition television to the Washington metro region.

The HDTV service sports programming from local broadcasters, including WJLA (ABC), WUSA (CBS), WRC (NBC), WETA (PBS) as well as premium channels HBO and Showtime. Comcast has rolled out the service to digital cable subscribers in Alexandria and Arlington, Va. To gain access to the high-definition programming, subscribers must have an HDTV-ready television.

The service is being offered to Comcast Digital Cable customers at no additional charge. On top of the HDTV channels, customers can receive more than 250 channels, including premium movie and digital music.

By the end of the month, Comcast expects to expand the service to Montgomery, Prince George’s and Charles Counties in Maryland; Prince William County and Reston in Virginia; and in the fiber optic upgrade areas of Washington, D.C.