This season's circus: excitement at a low pitch

Once again, the Ringling Bros. and Barnum & Bailey Circus has hit the entertainment trail, with two separate units touring the United States from one end to the other. Now in its 112th consecutive year, this enduring ''festival of family fun'' is as long and lavish as ever. And just as prone to self-congratulation, trumpeting each act with a ''breezy burst of bouncing ballyhoo'' --from the ''spirited, springing send-off'' at the beginning to the ''peerless parting shot'' at the end.

Leaving aside the hilarious, hysterical hyperbole, however, this is a bit of an off year for the ''greatest show on earth.'' Things were rather tame during a recent performance by the ''blue unit'' (one of the touring groups), which has opened its season with a long stint (through May 31) at Madison Square Garden.

The clowns, elephants, acrobats, daredevils, tigers, and such were all on hand. But the excitement stayed at a low pitch most of the time. While the youngest spectators were predictably starry-eyed, older ''children of all ages'' seemed to notice that the thrills weren't keeping pace with the sonorous spiel of the ringmaster.

To give credit where it is due, there were a few standout routines. Three acrobatic acts from Eastern Europe vied energetically with one another. The elephants were in good form. As always, the King Charles Troupe tore the arena apart with their basketball game on unicycles. And an aerialist named Miquel Vazquez gamely tried the ''unprecedented quadruple somersault'' after missing the simpler triple kind. Incidentally, he is billed as ''the only human'' ever to pull off the quadruple feat--making you wonder what other species has succeeded at the stunt.

For the rest, it was a rather mild afternoon. The clowns, trained dogs, and horse performers went through their paces mechanically. The tiger tamer, Charlie Baumann, lacks the flair of his better-known colleague, Gunther Gebel-Williams, who is now touring with the circus's ''red'' unit. And the highly touted daredevil Elvin Bale specializes in flashy stunts with little substance. First he rode a pointless ''mechanical monster'' --a funny-looking gizmo that belches smoke and a few flames, but seems less daunting than a typical tightrope or trapeze. Then he piloted a motorcycle across a highwire in the most academic-looking exercise of the whole show.

It all ended with a bang, as Capt. Christopher Adams revived an ancient circus spectacle by becoming a ''human rocket,'' shot from a cannon into a nearby net. Was it, in the words of the program, ''a booming, barely believable bombast of boundless, breakneck bravery''? No. But here, for a few seconds at least, was a touch of the dazzling pizazz the circus is supposed to be all about. The Ringling Bros. ''blue unit'' could use more of the same.