Longtime New York Giants public-address announcer Bob Sheppard intends to retire at the end of the season. Sheppard sent a letter about his retirement a few weeks ago to John Mara, the team's chief operations officer, Giants spokesman Pat Hanlon said Tuesday. Known for his relaxed, unhurried delivery, Sheppard began announcing Giants games in 1956 and remained a fixture with the team as it moved from Yankee Stadium to Shea Stadium to the Yale Bowl and finally to Giants Stadium in 1976. The New York Times reported in Tuesday's newspapers that Sheppard would step down as Giants announcer but will continue to announce New York Yankees games as he has for the last 55 years. A Yankees spokesman confirmed Sheppard planned to remain with the team.