MASTERS OF ATLANTIS. By Charles Portis. Knopf. 248 pp. $15.95.

CHARLES PORTIS is back with a funny and touching novel about an imaginary occult organization called the Gnomon Society. We follow Gnomonism from its inception after World War I, through its heyday in the Depression, and on through its slow attrition up to the present time. Much of the book's humor derives from the gap between the cosmic afflatus of Gnomonism and the fumbling lives of the Masters who profess it.

Portis, a former journalist who lives in Little Rock, Arkansas, is best known as the author of True Grit, a dialect tale of the old West which sold a million copies and was made into a movie starring John Wayne. True Grit was followed in 1979 by a picaresque comedy, The Dog of the South. Portis has a keen eye for the grotesque, and his books are filled with memorably odd characters. At times he reminds one of Mark Twain, at other times of Woody Allen. His basic stance seems to be that, in the hands of ordinary human beings, great ideas have no more meaning than silly hats.

At some stage in their lives, many people get the feeling that there should be some kind of key to the universe. The world seems like a mysterious whole, a unity whose essential secrets lie just beyond one's grasp. These numinous feelings may impel a person to delve deep into art, science, philosophy or religion. But a person with no great creative drive can easily get hung up on the numinous feelings themselves. Instead of finding difficult ways to make things clearer, such a person may opt for easy ways to make things more mysterious. This is the kind of person who, a few decades back, would have been likely to dabble in Madame Blavatsky's astral planes, G. I. Gurdjieff's laws of octaves, or Rudolf Steiner's writings on Atlantis. In general, these cults start with a few broadly suggestive principles -- notions like "All is One," and "As Above, So Below" -- and then swathe these precepts with layer upon layer of gauzy obfuscation. Gnomonism, as a parody of such cults, seems to consist of swathing alone.

All we learn about Gnomonism is that it is based on Pletho's Codex, supposedly from Atlantis, which has "several pages given over to curious diagrams and geometric figures, mostly cones and triangles." The leading exponent of Gnomonism is Lamar Jimmerson, respectfully known to his followers as "Mr. Jimmerson." Mr. Jimmerson writes a series of publications with titles like 101 Gnomon Facts, and The Jimmerson Spiral. Seekers agree that "The Rosicrucians had finer robes and the Brothers of Luxor had eerier ceremonies, but in the way of ideas that could not quite be grasped, neither of them had anything to touch the Cone of Fate or the Jimmerson Spiral."

TO BE as successful as the Masons, a cult needs more than numinosity and obfuscation; it needs a component of self-help and boosterism. This is provided by Austin Popper, Mr. Jimmerson's on-again-off-again assistant. During Gnomonism's go-go years, the 1930s, Austin Popper "led his followers in cheers and he played bouncy tunes on a windup phonograph, marking the beat with wildly swooping arms." Over the decades, Popper pops in and out of the Gnomons, pursued by the FBI and by the demons of alcoholism.

Mr. Jimmerson is a sincere and unworldly dreamer, though also a loser and a slob. As Gnomonism declines in the 1950s, he shuffles around the decrepit Gnomon temple, looking things up in his books, and wearing a "grin grown dreadful over the years." His wife and child leave him, and he spends the '60s dozing in a recliner chair, only to come up with the insight that the loose ends of his theories are all caused by the cosmic "Jimmerson lag," which has a numerical value of .6002.

Popper is a committed con-man, the kind of man who can speak of "holding down a good job selling bonds over the telephone from a boiler room." The book's funniest sequences all involve Popper. There are some lovely chapters where Popper, dodging the WWII draft, is living in a house in Colorado with Cezar Colescu, a Romanian crank who wants to refine gold from bagweed grown on mine-tailings. Popper and Golescu get tired of each other, and Popper takes it into his head that Golescu is from the Mid or the Far East. When a lady houseguest asks about Golescu, Popper says, "Oh no, he won't be joining us. Cezar is not a sociable man. He lies up all winter and lives off his hump. He'll be upstairs mashing his weeds. I'll leave a little pot of something outside his door that he can eat with his ivory chopsticks . . . He comes to us from the Caspian sea, and his name means 'not many camels.'"

Masters of Atlantis spans half a century, and watching thein characters drift through their pointless lives gives the book an autumnal, bittersweet flavor. The characters are fools and charlatans, but they are possessed by an enduring innocence, and by a touching human desire to know the unknowable. Although they occasionally cheat or dupe each other, they do this out of selfishness, rather than overt malice. By the end, they all seem like good guys to share a retirement trailer home with, guys who like to go to the beach and "ponder the two immensities of sea and sky."

Like all truly great comedies, Masters of Atlantis has a touch of sadness at its core. One suspects that, for Portis, the difference between Albert Einstein and Mr. Jimmerson is only one of degree -- both are weird, both are mortal.

Read this book, enjoy the belly laughs, and listen to the echoes in your skull. As two Gnomons put it:

"Do you know what's going on?"