In "The Big Show," NBC may have created the "Supertrain" of variety programs -- a whole lot of set and not much show. But prime time seems so funless right now, and so eminently snore-able, that "The Big Show's" hectic pastiche comes across, in context at least, as an entertainment rampage.

The program opens, at 9 tonight on Channel 4, with a fabulous traveling crane shot over a studio landscape that includes a swimming pool, an ice rink, a stage, potted plants, fountains and a few ornamental stalagtites. It's like hovering over the planet of Bad Taste or getting a quick visual history of Hollywood haywirism.

The program is a tentative mix of "Saturday Night Live" style satirical pieces, performed by an inadequately integrated stock company, and bombastic vaudeville of the sort that Ed Sullivan used to offer on Sunday nights or Nick Vanoff -- producer of "The Big Show" -- onced presented on ABC as "The Hollywood Palace."

Perhaps it would help if fewer of the acts were so doggedly motley. Peggy Fleming is icier and less embraceable than the stuff she skates on. Ballet star and Russian defector Alexander Godunov is strikingly dull and uncharismatic. Water ballet, roller-disco and ice skating routines prove woefully silly.

But in the second hour of the two-hour premiere, Steve Martin drops casually by to show films of his visit to Terre Haute, Ind., and this is very funny stuff, as are some of the sketches featuring such resident performers as Graham Chapman of the Monty Python troupe and American Indian comedian Charlie Hill.

There is essentially only one element, though, that keeps "The Big Show" from being merely lots of pieces of videotape spliced together, and that is the presence of Steve Allen as guest host, accompanied by the ubiquitous Gary Coleman of "Diff'rent Strokes," whom Allen works with graciously and patiently.

The lack of a continuing host is immediately a drawback to a show like this; in the case of Vanoff's "Palace" hour, the theater itself was a kind of continuing character and provided a unifying personality of its own."The Big Show" suffers from a lack-of-identity crisis.

And Allen will be a hard act for other guest hosts to follow. The agility, the finesse and the energy he brings to this job give the program pick-me-ups when it most needs them. After the Steve Martin segment, the best on the show, Allen looks into the camera, says "We'll be right back," and does his trademark salute to the audience, and one realizes how much this kind of affable, effortless professionalism is missed on television.