Bobo the Bear, left, Rizzo the Rat, the Great Gonzo, Nathan Lane as Officer Meany, Pepe the King Prawn, Kermit the Frog and Fozzie Bear are all part of the adventure when the Muppets take on the task of getting letters to Santa.

NBC / Eric Liebowitz

The Muppets fly, but they don’t soar in A Muppets Christmas: Letters to Santa.

The NBC special, premiering at 8 tonight, represents mediocre Muppet mirth.

Mediocre is better than nothing, but these show-business legends deserve better.

The mundane script sends them on the last-minute errand of getting letters to Santa. The nadir is a trip through airport security, where they deal with a bossy security guard (Nathan Lane).

The commercial breaks are abrupt, and the production numbers lack the old Muppet pizzazz.

Most big-name guests have meager duties. Lane fumes. Whoopi Goldberg drives a taxi. Neighbor Jane Krakowski frets. Airline employee Uma Thurman looks glamorous, which is no sweat for her.

Some old TV favorites have more to do. Jesse L. Martin of Law & Order plays a postal carrier, sings and headlines a daffy production number saluting the post office. Sopranos vets Tony Sirico and Steve Schirripa portray mob figures who get tough with Pepe.

Make no mistake: Shrimp Pepe emerges as the star. His sarcasm spices the show, and he displays jumbo talent in going through security and swooning over Thurman.

Other Muppet favorites carry the dramatic action. Kermit is torn between placating Caribbean-bound Miss Piggy and helping his friends with the letters. Gonzo mopes about those letters before suggesting a trip to the North Pole.

Paul Williams contributes some lovely songs and puts in an appearance at the North Pole. New York Mayor Michael Bloomberg pops up in an amusing cameo. Richard Griffiths of Harry Potter fame is perfect casting as Santa.

The Muppets are forced to travel on the wing for their flight, and that’s just a sign of where this special goes wrong. They rate first class. But at least Pepe keeps the Muppet merriment marvelous.