NEW YORK - S. Epatha Merkerson, the senior member of the "Law & Order" cast, is leaving after the show's current 20th season.

Merkerson, who joined the NBC drama in 1993 as New York police Lt. Anita Van Buren, has decided to exit after 17 years, according to a person close to the show who spoke on the condition of anonymity because that person wasn't authorized to speak about cast changes.

The 57-year-old Merkerson is an Emmy winner for HBO's 2005 film "Lackawanna Blues" and, early in her career, played Reba the Mail Lady on "Pee-wee's Playhouse."

As Merkerson prepares to depart "Law & Order," it awaits news of whether it will be back. A renewal for next season would make it TV's longest-running drama. It currently ties "Gunsmoke" of a generation ago.