BOOK REVIEW / HUMOR : When It’s Too Important to Be Serious : ALL THE TROUBLE IN THE WORLD: The Lighter Side of Overpopulation, Famine, Ecological Disaster, Ethnic Hatred, Plague and Poverty <i> by P.J. O’Rourke</i> ; Atlantic Monthly Press $22, 340 pages

The only thing more unpleasant than a well-versed liberal is an intelligent conservative. In the case P.J. O’Rourke and “All the Trouble in the World” we have an intelligent conservative who’s also effete, sartorially smug, in a state of perpetual preppiness and somewhere to the right of Judge Robert Bork, traveling to Haiti, Somalia, Bangladesh, Vietnam, what used to be Yugoslavia, what used to be Czechoslovakia and what used to be a pristine rain forest before he got there.

During the course of these meanderings O’Rourke faithfully reports to us in great and jaundiced detail all of his daily observations, interactions and movements, including, occasionally, bowel.

Will the result be merely a tawdry travelogue roughly similar in spiritual timbre to Rush Limbaugh walking his pet stomach over the airwaves of America? If you suspect the answer is yes , you’d not only be wrong, you’d be in serious danger of missing one of the funniest, most insightful, dead-on-the-money books of the year.

“All the Trouble in the World” is O’Rourke’s indefatigable, not to say quixotic, effort to show us “the lighter side of overpopulation, famine, ecological disaster, ethnic hatred, plague and poverty.” It is work that succeeds, quite possibly in spite of its author. Indeed, O’Rourke is probably at his best when he steps outside the casino of politics and shows that rare, seemingly unconscious glimpse of himself and, God help us, ourselves as well.

Trekking through the Amazon rain forest, O’Rourke asks the metaphysical question: “Why do the eco-tourists have neon-blue hiking shorts? And fluorescent-purple Windbreakers? Caution-signal-yellow sweat socks? Craps table-toned fanny packs? HoJo tinted luggage? T-shirts the hue of sex dolls?” He ponders the connection between the love of nature and the colors not found therein.

The people who live in the rain forest also come in for close scrutiny. “Most of the locals seem to make their living in the open-air market,” he asserts, “selling each other the same enormous catfish.”

As he leaves the Amazon, the author provides us with some concluding thoughts about what the world might be like without the rain forest. “I gather that, if the rain forest disappears, we’ll have to get our air in little bottles from the Evian company, and biodiversity will vanish, and pretty soon we’ll only have about one kind of animal, and with my luck that will be the Lhasa apso. . . . Furthermore, we’ll never discover all the marvelous properties of the various herbal treasures that are found in the rain forest, such as Ben & Jerry’s Rainforest Crunch.”

Equally entertaining and enlightening are O’Rourke’s accounts of his travels in Vietnam, Somalia, Yugoslavia, Czechoslovakia and Bangladesh, from which one can learn things that a lifetime of watching CNN may not reveal. Of course, as the author makes clear at one point during a visit to a particularly horrific slum in Haiti, “you can’t smell television.”

Possibly because Haiti seems to be the flavor of the month, O’Rourke’s observations of his sojourn there appear to be all the more compelling. “Haiti,” he says, “is integrated in a way not seen in the United States except in soft-drink television commercials.” He describes a certain section of Port-au-Prince as burned out and boarded up almost like the downtown area of an American city. The author also refers to one of Haiti’s former dictators as “Roseanne Arnold with infantry.”

Much impressed with the spirit and charm of the Haitian people, O’Rourke, after an all-night voodoo celebration, proposes this trade to them: “You sail north. And we’ll get a bunch of crabby families in Winnebagos, drug smugglers, Disney executives, Palm Beach divorce lawyers, 2 Live Crew, Burt and Loni, time-share condo salesmen, Don Johnson, Miami Beach aerobic instructors, William Kennedy Smith, kvetching retirees, teen-age gang members, and wounded German tourists, and we’ll send them back to Haiti on the same boat.”

O’Rourke may well take a measure of ‘90s microwaveable heat for this provocative book but, as he well knows, some things are too important to be taken seriously. And I also suspect that somewhere in his travels he’s heard the old Turkish proverb: “When you tell the truth, have one foot in the stirrup.”

Happy trails.