BOOK REVIEW : Thinking About a Nation’s Complexity : BROWN SHOE <i> by Rick Slone</i> ; Random House $20; 342 pages.

You have to get out your map of Peru for this one. (The country is never directly named, but the suburb of the capital in question is Callao; the guerrilla hero makes an escape to Iquitos on the other side of the mountains. It’s Peru, all right.)

The time is the present. The narrator-observer is Bobby Shafto (who, presumably--as in the old nursery rhyme--has gone to sea, with silver buckles on his knee and ended up somehow in this coastal city). Bobby has run out of money and signed on as a cook in the best restaurant in town, run by a raffish dude named Blacky.

After hours, they do a few lines of cocaine, drink good wine, kid around, play some good music. Bobby is a photographer--just flirting now with this profession--killing time in the restaurant business. The lives that these two lead are intensely personal, even though all around them, the country is going to hell in a handbasket.

Across town, a thick-necked thug, Col. Rinaldi, toys absently with his very young mistress, Nina. Rinaldi and the girl go way back; he was a friend of her father, she was engaged to his son, who has been recently blown up--the word is--by a guerrilla outfit called Moreno. (The real question in this novel is: How much does the Moreno resemble the Shining Path group in Peru?)

Without giving the plot away, I can safely say that Blacky in his gourmet restaurant is very close to the Moreno, and when newspapers begin to report that Roberto Gavilan, the leader of the movement, has been killed in his mountain hideout, Blacky persuades Bobby, the photographer and would-be journalist, to head on up into the mountains, talk to Roberto, take his picture and come back with concrete evidence that Gavilan is still alive, to give the common people hope.

(Again, yes, we’ve seen movies like this, starring James Wood, or Nick Nolte, or even the old and wonderful classic, “Viva Zapata,” in which Joseph Wiseman utters the best line of his acting career: “Cut off the head of the snake and the body will die!” But this is different.)

Gavilan is the “head of the snake” this time, living precariously in the beautiful, hostile mountains, but the snake itself is feeling mighty poorly. Roberto has, at most, a dozen men; at least, seven. These men are starving. The unpleasant truth is: The mountain peasants detest the Moreno. (They detest the army too, but figure they wouldn’t be there if it weren’t for the guerrillas.)

So here’s the lineup: Bobby and Roberto, so close in some ways that they carry similar names. Blacky as the urban arm of the Moreno, so close that they too carry almost the same name. A romance which has developed between Bobby and Nina and which causes the thuggish colonel to revert to his most animalistic forms of demonic evil. And lots of “Peruvians” hanging out, trying the best they can to live their own lives with some kind of direction and dignity.

The author brings up some very interesting points: How can somebody “save” the peasants of any country if the peasants are unevolved, dead to the world and hate their would-be saviors? Rick Slone also suggests a kind of triangular society in which guerrillas, cocainistas and the military exist in a symbiotic relationship. Each could not exist without the other two. (But even given that symbiosis, you still get to choose which corner of the triangle you’d rather be in.)

There’s also another very delicate element here--the contempt with which the old rich, the aristocrats, regard poor Col. Rinaldi. Certainly Rinaldi is a beast, but his mindless, vengeful atrocities keep the aristocrats safe, even though they too detest him, as much as the peasants hate Gavilan.

The author is an unexpected master of unexpected scenes. Nina, horrible Col. Rinaldi, his attractive wife and Bobby-the-journalist (who cooks up a gourmet feast) find themselves together on the old Rinaldi family ranch. The four manage to fit themselves into a cordial group. The restaurant scenes as well are terrific. The racetrack scenes--all marvelous.

The plot gets a little screwy in the last 50 pages, but Slone is interested in far more than a plot. He’s showing us a world, or political stereotypes of right and left. He’s asking the reader to check out the amazing complexity of the Third World and to--if it’s not too much trouble--think.