When the creator of “First Monday,” debuting at 9 tonight on CBS, decided to make a legal drama, he went straight to the top.

“First Monday,” which moves Friday to its regular 9 p.m. time slot, takes viewers to the Supreme Court, not only into the courtroom but behind the scenes as well.

Don Bellisario is also behind CBS’ hit “JAG,” which features pretty young lawyers in dress whites. His new series instead showcases mostly craggy old judges in black robes.

The drama focuses on Joe Novelli (Joe Mantegna), who’s just starting as an associate justice on the high court. The court is evenly split between liberals and conservatives, and everyone is fretting about the direction in which Novelli will lean.

While “JAG” is more about action and mystery, “First Monday” is a series about ideas, and that requires the viewer to work a bit. In the second episode, the court will tackle the abortion issue.

But while “First Monday” handles the courtroom issues well, it needs to beef up its characterization. We find out about Novelli, his wife and his two teen kids. But viewers learn little about his fellow justices, including James Garner as the chief justice and Charles Durning as his conservative cohort. With such a talented, veteran cast, there has to be more development of Novelli’s workplace.

“First Monday” isn’t without its perky young characters, however. They are in the person of Novelli’s law clerks, played by Hedy Burress, Randy Vasquez (a recurring presence on “JAG”) and Christopher Wiehl. They write those all-important background briefs to help Novelli make his weighty decisions.

Still, “First Monday” has potential, based on its subject matter and cast. With Bellasario’s track record in steadily developing dramas, viewers should definitely weigh “First Monday” carefully.