A small group of intellectual snobs has found refuge at an unsupervised think tank called the Institute for Advanced Concepts. Hermetically sealed from the glare of publicity or the inhibitions of social responsibility, they allow their demented brains to roam free. They conduct Frankensteinian research (a genetic cross between man and cockroach) and perpetrate hoaxes at the expense of an oblivious nation, like jamming Nielsen boxes so that all the dumbest TV shows get the highest ratings.

So begins Marshall Brickman's "Simon," opening today at area theaters. Brickman -- an erstwhile folk singer (with The Tarriers and The Journeymen) and gag writer (for Alan Funt, Johnny Carson and Dick Cavett) -- achieved renown and an Academy Award by collaborating with Woody Allen on the scripts of "Sleeper," "Annie Hall" and "Manhattan."

He makes his solo debut as a writer-director on "Simon," a sputtering but diverting satiric fable which stars Alan Arkin as a nutty professor, and Simon Mendelssohn, whose pretensions allow him to be brainwashed into the delusion that he's a prophetic visitor from outer space.

Our guide to the plot is the think tank's snob-in-chief, Carl Becker, portrayed with smug perfection by Austin Pendleton. He introduces us to a quartet of wittily cast accomplices: William Finley (Brian De Palma's erstwhile Phantom of the Paradise) as the gawky, multibespectacled Fichandler; Jayant as the exotic Barundi; Wallace Shawn as the dumpy Von Dongen; and Max Wright, the most distinctive and amusing cracked egghead of them all, as the deceptively bland Hundertwasser.

The scheme that entraps Simon is inspired by a newspaper item revealing that a majority of Americans believe in the existence of extraterrestrials. The IAC staff concludes: "Why not give the public what it wants? The Institute's supercomputer, a feminized version of Kubrick's HAL ("2001" is the inspiration for more than one gag) shaped like a giant telephone receiver, selects the ideal dupe -- Simon, an obscure, orphaned, fame-hungry psychology prof at Columbia.

Lured to the institute, Simon is flattered by the attentions of the staff and seduced by a ringer, Madeline Kahn as a trollop hired to pose as a fellow researcher. Following almost 200 hours of immersion in a sensory deprivation tank, Simon emerges believing he's an alien humanoid whose superior intellect qualifies him to make authoritative pronouncements on terrestrial society.

Brickman's plot seems to combine elements of "The Magic Christian" and "Sleeper." The similarities to the latter -- and the tenor of the verbal humor -- suggest that Brickman and Woody Allen have become such alter-egos that it's impossible to isolate one's style of wit from the other's.

Some undesirable affinities are also apparent. Although intellectual snobbery is the ostensible satiric target in "Simon," Brickman's witticisms often reflect the value systems of cosmopolitan know-it-alls who can't help articulating their sense of superiority to mere fads or minor cultural nuisances.

For example, there are more than enough wisecracks ridiculing television programming and Muzak. Clever and literate as the repartee in "Simon" frequently is, it also reminded me of why I was bugged by a lot of the gratuitous joking in "Annie Hall." Allen and Brickman can't quite shake off the snobbish tone of the Alvy Singer character, although they made a concerted effort to contradict it in the subsequent Allen role in "Manhattan." Judy Graubart, cast as Arkin's patient, rational fiance, ultimately rescues Simon from his messianic follies. pBut the script is still littered with a kind of cheap shot humor that inflicts only flesh wounds on the sitting ducks of mass culture.

"Simon" also clarifies the advantages Allen enjoys in being both humorist and performer, especially when the plot evolves into a chase comedy which recalls "Sleeper" but keeps running out of gas. Brickman is not able to embody his own jokes: When plot invention temporarily fails, he cannot fall back on a familiar, personalized comic identity.

Despite its hit-and-miss nature, "Simon" is bright and promising enough to make you want to see more from Brickman. As a director, he's begun at a level of pictorial sophistication that Allen didn't achieve until his third or fourth feature. "Simon" looks exceptionally crisp and concentrated. It appears that Brickman is capable of a technical finesse that might recall the pleasures of Ernst Lubitsch if and when he gets his plots and casting sufficiently coordinated.

But "Simon" absolutely needs a comic star once the focus shifts to the title character. Alan Arkin is an accomplished character actor with certain humorous gifts, but he is not first and foremost a comedian. The script is full of minor miscalculations and misfired jokes that can be forgiven or canceled out by the winners. Brickman can't compensate for the fact that when the chips are down, this particular premise requires a performer who is innately, irresistibly funny.

Robin Williams -- who will soon make his film starring debut as Popeye -- has the kind of talent that might have put "Simon" over the top. Whether Brickman could work in harmony with such a manic, intuitive comic personality is a matter of conjecture. Maybe it's worth finding out. One can also envision Steve Martin as an effective Simon. This script would certainly have brought him more respect than "The Jerk," if only a fraction of its wealth.

If Brickman is leery of new comedians, and there might be sound reasons for being leery, it would probably be advisable to concentrate on forms of dramatic comedy needing character acting more than a unifying, dominating star presence.The expert supporting performances in "Simon" suggest that Brickman will be more successful placing his eggs in several baskets. One retains more vivid and pleasurable impressions of the peripheral figures -- Pendleton and his cohorts, Graubart, Fred Gwynne as a fuming Army officer, Adolph Green as a communard -- than of the central character.

"Simon" is no triumph, but it has its moments and justifies a modest, patronizing investment in Brickman's filmmaking future. As Andrew Sarris has pointed out, "30 or 40 minutes of genuine intellectual humor is 29 or 39 minutes more than one will find in 'The Jerk,' so let us be grateful for little favors."