Richard Eder : LAKE WOBEGON DAYS by Garrison Keillor (Viking: $17.95; 336 pp.)

It says something about our untied times that Garrison Keillor’s Cockaigne, his Oz, his Neverland, should be a meticulously invented world of the ordinary. For years, quirk by quirk and shingle by crossbeam, he has been assembling for his “Prairie Home Companion” public radio program the mythically humdrum community of Lake Wobegon, Minnesota.

“Lake Wobegon Days” transforms Keillor’s radio monologues into a series of reminiscences about this imaginary community whose down-home normality strikes us--and him, I suspect--as about the most exotic thing going. “Tall tales about short happenings,” its subtitle could be. Keillor’s folks are Paul Bunyans of the everyday.

Lake Wobegon is not on the map but, Keillor tells us, this was only because of a land surveyor’s error. The railroad never went through, so a spur was built. One of the biggest days in the town’s history was the day the Empire Builder was switched onto it by mistake and arrived, full of celebrities; all of whom had to be backed out again.

Backward-towed celebrities--it stands for Keillor’s amiably sardonic view of American history and culture. Our public life of big and evanescent events is at the wrong end of his railroad spur. Instead, he gives us this wacky and stolid Norwegian-American small town, whose site was visited in 1836 by an explorer on the hunch that it might be the headwaters of the Mississippi.

“Then something about the place made him decide he was wrong,” Keillor writes. “He was right, we’re not the headwaters, but what made him jump to that conclusion? What has made so many others look at us and think: It doesn’t start here!?”

Nothing does start here. “We are what we are” is the town motto, and Keillor endows Lake Wobegon with a history, a geography, a population and a style of life that damp down any suspicions of Promethean fire. The Pretty Good Grocery stocks items that are only reasonably fresh and that eschew fanciness. Wobegonians can drive to the next town for a wider selection; but the local shopkeeper, plumber and garage mechanic serve on the Rescue Squad, so nobody thinks of driving off too often. Loyalty is the watchword.

The works and days of Keillor’s Wobegon are beguiling, comical and, in their refractory way, instructive. His book is filled with good things, but it has its problems. One is stylistic. The effort to transform the 20-minute monologues of his radio program into a more sustained written form doesn’t work entirely. Sometimes a point is hammered home with a persistence more suitable to the ear than to the eye.

More seriously, if the book lacks the momentum of authentic fiction, it also lacks the anchor of authentic documentary. It is a pastiche, and a very talented one; but there are times when the whimsy frays. The details accumulate charmingly enough but fail to carry matters along. Shortening would help: The author uses an instrument a bit too cumbersome for his particular kind of comic vision.

The vision is at its best in the contradiction that Keillor quietly presses upon us. Fixed in its ways and suspicious of flamboyance as Lake Wobegon may be, its genius is in the unpredictable and self-invented characters it produces.

There is the man who invents the local Fourth of July pageant, where everyone dons red, white or blue caps and stands in formation to produce an American flag. Of course, only the organizer, standing on a ladder, can see the result. Consequently, the flag loses stars and stripes as the participants climb up to see for themselves.

There is the local priest, Father Emil, who goes regularly to the local diner in the vain hope of having “a secular lunch”--one, that is, where some neighbor will not come up to talk about religion. There are Mr. and Mrs. Luger who, each spring, are caught up in a fever of vegetable planting, and by late summer are inundated.

“The Mister reaches for the razor in the morning, he picks up a cucumber. Pick up the paper, underneath it are three zucchini. They crawled in under there to get some shade, catch a few Z’s, maybe read the comics. Pumpkins are moving in to live with them. At night they check the bed for kohlrabi. Turn out the lights, they hear rustling noises downstairs: a gang of cauliflower trying the back door.”

There is old Mrs. Krueger who lives by herself and calls the police because she suspects a bat has got in. When they arrive, her radio is playing a Glenn Miller program. Back in their cruiser they try to find the station; it doesn’t exist. Only occasionally does Keillor allow such a ghost in. His Lake Wobegon originals are rooted in the most modest kind of life, resistant to fads and additives. Real flavor, he suggests, comes out of soil that is unassisted and let be.