'The Greatest Show on Earth' celebrates 100 years of circus fun

It's just 100 years since five brothers from Baraboo, Wis., kicked in their savings and launched the first performance of the Ringling Bros. Circus - which later hooked up with P. T. Barnum and his partner James A. Bailey and became the self-proclaimed ''greatest show on earth.''

How is the circus celebrating its centennial? Just the way you might expect - by following its entertaining traditions to the letter, merely adding some extra frippery to let us know it's an important anniversary.

That frippery is most extravagant during the pageants that close the two halves of the show - usually dull affairs, in my view, but enlivened this year by sumptuous staging, complete with a burst of modest fireworks. For the rest, it's 21/2 hours of the usual inspired nonsense, with the peaks and valleys of interest.

Checking out the circus's ''blue unit'' on opening night of its new edition (there's also a ''red unit'' with different acts), I was most taken with a spectacular display of gymnastics near the beginning, performed by a group identified in the program only as ''an ambitious assembly of agile athletes.'' I also enjoyed, as always, the King Charles Troupe from New York City, now in its 16th year of playing circus-style basketball on unicycles. And I got the usual bang (!) from Captain Christopher, who allows himself to be shot from a cannon twice or thrice a day.

Though the clowns seem to have more energy and audacity than in some past years, most of the rest of the show is standard fare. The elephants are in good form. A trained dog-and-dove act draws some ''oohs'' and ''ahs.'' Animal tamer Wade Burck puts white and yellow tigers through impressive paces without getting bitten. The resident little person, billed this year as Mighty Michu, blends into the show without slowing it down, as he sometimes has in the past. Miguel Vazquez, of the Flying Vazquez quartet, gamely tries (and failed, on opening night) the quadruple aerial somersault, which he is reputed to be ''the only human ever to conquer.''

Other acts range from the Atlas Highwire Troupe and contortionist Nellie Ivanov to the Lilov Bears and no less than three teeterboard routines. All will be on view at Madison Square Garden through June 3, then begin an extensive national tour.

A century old, and still going strong!