Calvin Trillin was a floater before he became a star reporter for The New Yorker. His novel's hero, Fred Becker, is a floater now and hopes to remain one. Once, he hoped to be a singer in Broadway musicals, but he didn't have quite enough voice. Now, he occupies a rent-controlled apartment (which may be the only cogent reason for staying in Manhattan) and earns his living at a weekly news magazine, drifting from one back-of-the-book section to another -- Religion this week, Business or Lifestyle or Education next week -- as the patterns of vacation and sick leave require.

He does not enjoy Religion and tries to get out of it by inserting "alleged" before references to various cherished events in religious history, but for the most part the back of the book is a pleasant place to float.

He may be writing an article about obscenely sculptured shrubbery at singles apartment houses; becoming an overnight expert on an abstract impressionist painter; working on stories about Californians drowning in hot tubs, or sex-change operations as a stimulus for tourist trade, or the imminent extinction of some endangered species dear to the publisher's heart. If the job doesn't quite call for a renaissance man, it certainly helps build dilettantes.

In contrast, Becker dreads several career possibilities: a transfer to Washington, D.C., which is simply unpleasant; a permanent position in the Foreign News section, where he would have to write basically the same story about Cyprus week after week; a promotion to bureau chief in Ottawa, where nothing ever happens and it is very cold; an appointment to Medicine, where he would have to write about things like the pancreas.

If he ever stops being a floater, Becker wants to do it by writing a blockbuster novel -- like Dick Chiles, "a former writer in National News who had hit it rich with a novel based on a Palestinian guerrilla plot to kidnap the society editor of The Washington Post -- 'A Long Way From Georgetown.'"

The fact that The Washington Post has no employe with the title of society editor does not stop Chiles' career. His "second blockbuster was about a crazed English professor who kidnapped the nation's most famous talk-show host and refused to release him 'until everyone's sentences parse.' By his third book, Chiles had only to show the publisher a one-sentence synopsis of the plot ('It's about a kidnapping') to get what was reputed to be a $300,000 advance, a 60-40 split on the paperback sale, and a permanently reserved table at Antonio's, a midtown Italian restaurant favored by the publishing set."

While he dallies with such dreams of glory, Becker is happy enough at the magazine. Andy Wolferman, the magazine's chief purveyor of internal gossip and hatcher of elaborate office intrigues, is less positive: "Working so closely with the same people week after week was, as Andy Wolferman often said, 'like being snowed in all winter in a village populated by particularly neurotic villagers,' but Becker had become accustomed to the village. . . . He had long taken it for granted that the internal goings-on at the magazine were more important than the events the magazine wrote about. Sometimes he daydreamed about a magazine that dealt with the magazine."

Lacking the advertising budget to finance such a periodical, Calvin Trillin has settled for a mere book about a weekly magazine, but he has populated his self-enclosed world with some splendidly vivid if one-dimensional characters.

There is, for example, Milt Silvers in Education who "collected eccentricities relentlessly. He lived in a converted tugboat under the Brooklyn Bridge and always drove some exotic vehicle like a surplus British army halftrack. Becker couldn't remember a time when Milt Silvers owned an ordinary automobile or had a pet more conventional than an iguana."

And there is editor-in-chief Woodrow Fenton, whose conversation and editorial guidance are limited almost exclusively to saying "Gosh," "Golly" or, occasionally, "Gee whiz."

There is "Doc" Kennedy, the Medicine writer, who tends to catch the symptoms he describes, and a host of minor characters such as researchers who insist on accuracy (of all things) or editors who earn their living by asking, "Is that a trend?" If three things of the same kind have happened within living memory, it may be a trend. And if no trends are visible at the moment, the magazine is capable of creating one.

These may sound like the ingredients of a situation comedy, and that is approximately what Trillin has created -- except that his writing is genuinely funny (sometimes to the point of laughing aloud) and his book doesn't seem to have much of a plot. Like Fred Becker, the novel seems to spend most of its time floating from one interesting, inconclusive situation to another.

Then suddenly, around page 180, with only two dozen pages to go, Trillin springs a literary trap, and it turns out that his loose-looking novel is tightly plotted. All the loose ends that were apparently thrown in only for their laugh value are suddenly knit together into an intrigue subtle and devious enough for a suspense novel two or three times its length.

In its own small way, "Floater" is a literary tour de force. But that's not the real reason for reading it. The reason is that it is very funny.