A superbly reliable circus spectacular -- from Ringling Bros.

Nobody can accuse the ''greatest show on earth'' of shifting direction with every popular breeze. When it comes to basics, the Ringling Bros. and Barnum & Bailey Circus still leans comfortably on old reliables - the clowns, daredevils, prancing elephants, and educated tigers that have been its main attractions for as long as anyone can remember. Even the show's occasional gestures toward recent fads and fancies don't manage to be very fresh: This year's mascot, for example, is the Pink Panther, hardly a newcomer to the entertainment scene!

But as every child knows, a sense of ceremony and dependability is what keeps the circus cozy and familiar; like an old friend, the show is essentially the same every time you run into it, with just enough differences to make each visit distinct from the last. Lending further variety-within-continuity is the Ringling practice of maintaining two different shows (the ''red'' and ''blue'' units) that alternate their touring itineraries. This year was New York's turn for the ''red unit,'' which is playing Madison Square Garden through June 5, after which it will proceed with its annual travels.

Opening night found the proceedings as big and bombastic as ever, and still energetic enough to open with the kind of blockbuster attraction that might serve as climax to a lesser show. I refer to the ''mystifying motorcycle maneuvers'' of the Urias Troupe, a Brazilian duo who race their cycles around the inside of a circular ''globe of death'' while a young woman stands inches away in the center of it all. It's a brief act, but it sure puts you on your toes.

Other high points, for me, were the ''breathtaking balance bravado'' of the Fearless Bauers, a Swiss trio who cling to ''sway poles'' at ''the very apex of the arena,'' and the high-wire stunts of the Carrillo Brothers from Colombia, whose accomplishments are indeed - to quote the program again - ''handsomely handled at harrowing heights.''

A group called the Leaps does just that, jumping off a sort of runway with enough momentum to soar over the backs of elephants. Sundry teeterboard troupes, all from Bulgaria for some reason, do their stuff with style; and the Flying Espanas perform the requisite somersaults while hurtling from one trapeze to another.

The star of the ''red unit'' is again Gunther Gebel-Williams, the touted animal tamer, and he has his family along. At one point he puts horses through their paces in Ring 2 while wife Sigrid and daughter Tina do the same in Rings 1 and 3. Also on hand is 12-year-old son Mark Oliver Gebel, whose trained goats could use a little more training. Gunther himself opens the show's second half with his tiger extravaganza, and follows it up later with a pair of elephant acts - standard circus material, but elegantly performed, and marked by what seems to be a real affection between the trainer and his beasts.

Other events range from Hall's Baboons to Miss Tina's Russian wolfhounds, from the shenanigans of clown Lou Jacobs to the acrobatics of his daughter, Dolly. There's something for everyone, as always, and plenty of signs that the Ringling show will continue to thrive until it's far older than its current 113 years.