AFTER weeks of making Dick Wolf wait for a decision, NBC has officially told him to go ahead with production on a 20th season of “Law & Order” (starring Sam Waterston).

The veteran crime drama, which moves to Fridays at 8 p.m. this fall, will tie “Gunsmoke’s” record as being the longest-running dramatic series on TV.

NBC also announced that “Law & Order: Special Victims Unit” is getting another season, too, with a timeslot change of its own. It will air Wednesdays at 9 p.m., with encore presentations on Saturdays at 10 p.m.

Two long-time fan favorite shows that didn’t make the cut were “Medium” and “My Name Is Earl.” —