Steve Martin makes a great joke out of appearing to enjoy life too much. His first network special, "A Wild and Crazy Guy," on NBC tonight suggests Martin is also spreading himself too thin too fast, but he continues to be an incorrigible radical in the vanguard of the loony liberation movement. He brought funny comedy back.

"I love wondering about things that have no point," he says.

Unfortunately, the one-hour special, at 9 on Channel 4, has been organized as a series of interruptions, with director Gary Weis repeatedly cutting away from a taped Martin concert for filmed vignettes that often clunk to laggard, freeze-frame ending. It's a little like seeing Martin through the fragmented prism of an Eyewitness Newscast.

The awkward structure was probably dictated by dilemma: Martin's fans expect his traditional bits - allegations of embezzlement against his cat, serpentine balloons and the arrow through the head - the way a Judy Garland crowd insisted on "Over the Rainbow." At the same time, he doesn't want to be known as the Johnny One Note of Comedy. The show represents an unsatisfactory but fitfully hilarious comproise.

Martin's oversize and overeager dumb-cluck grin, so enthused that his face dcan hardly contain it, may be the prevailing comic iron of the late '70s and when it bursts through during the show, it redeems thin material and turns patty-cakes into punch lines. Style is substance and medium is the message.

Somehow unknowing and all-knowing simultaneously, Martin pops up in a series of quick skits whose theme is usually outlandish thick-headedness. In a yellow diaper at a suburban front door he asks, "Did anybody call for a doctor?" On behalf of "Save a Dump," he warns of a plot to turn refuse refuges into unsightly green parks.

And when, as the king of the turtle-boys, he conquers a bucking tortoise while sporting a green gingham dress, it's only because his gal had asked, "Steve, would you wear something of mine for good luck?"

The spotlight proves solim; Milton Berle, Bob Hope, George Burns, Johnny Cash and even Henry Winkler drop by, but so briefly they hardly register. The show is all Martin's.

Those who discovered him early may be tiring of him now, and he risks, becoming the most merchandized figure of fun since R2D2, but Martin has brought the immortal rube up to date in a manner that remains idiotically infectious and invigorating.