A Legionnaire’s Experience: From Romance to Escapism : A MOUTHFUL OF ROCKS Modern Adventures in the French Foreign Legion<i> by Christian Jennings(Atlantic Monthly Press: $18.95; 240 pp.) </i>

He was the puny kid in the old Charles Atlas pulp magazine ads, the one who had sand kicked in his face by Mr. Universe before the big bully walked off the beach with the girl.

He was the prototype for a modern American Skinhead, the guy who loved the way weapons could compensate for lack of natural stature or authority. He was a forger, a part-time soldier and a stabbing victim before reaching his majority.

Then Briton Christian Jennings, so well on his way to being a ne’er-do-well, joined the French Foreign Legion, following the historic footsteps of Capitaine Danjou as well as the Hollywood footsteps of Cary Grant.

Jennings’ experience, told in prose both evocative and inelegant --”He took my passport off me and told me to sit down”--is the ultimate escapist literature. Literature, because Jennings tells a new travel story to a world that has now been almost everywhere else. Escapist, because the author’s whole reason for enlisting was to get away--from family, prior failure and away from the world where adults are expected to make their own everyday choices.

The Legion, true to its myth, still offers incredible sanctuary plus the promise of a new life untainted by past behavior or even past identity. Jennings was told that he could adopt a new name, a different nationality and a fresh birth date. Losing himself, he could find security: “There were no emotional worries because we hardly saw any women apart from prostitutes, no financial problems because we were all paid the same amount on the same day every month. The orders posted . . . every morning told us what to wear and where to be at any given time, we had no civilian clothes as they were forbidden, and we all looked alike with our shaved heads.”

The Legion, true to its myth, still offers prospects of combat in another country on another continent, with a history of heroism in Morocco, Mexico, Madagascar, Indochina, Vietnam and, more recently, Chad. Now numbering about 10,000 men from all over the world--their tattoos more revealing than their reminiscences--the Legion maintains an appetite for strong wine, compliant women and boisterous song: “Singing was intended to enhance the bond between us, for by reciting verses and lines about the Legion, past and present, we were reinforcing our beliefs in the traditions we stood for.”

Those traditions, alas, included twice-a-day inspections for recruits, a ban on speaking languages other than French and violence as the accepted way to establish discipline. The rocks in the book title refer to stuffing stones in the face of a lapsing Legionnaire, an almost benign punishment compared to the beatings, gougings, stompings and sexual abuses suffered by Jennings and his colleagues.

From the beginning, the Legion was a military of misfits. Prince Louis-Philippe created the force in 1831 as a dual way to do good for France. “Undesirable elements” at home would have a place outside Paris to go and those same people would be the cheap labor to build and defend a new colonial empire.

They did. A motto painted on a 19th-Century barracks wall became the credo: “Legionnaires, you are soldiers in order to die, and I am sending you where you can die.”

Desertion was and is a mortal sin, punishable by battering, bludgeoning and naked imprisonment if not by death.

But an escape artist like Jennings, being appropriately trained as a paratrooper, was not deterred. He became tired of taking orders and accepting outrages from two corporals. So, one night in Camp Amilakvari, in between the civil wars of Somalia and Ethiopia, Jennings climbed out over the barbed wire, disturbed a mountain family of baboons, stumbled down a steep rock slope and found himself in the scrub desert outside Djibouti. At first he was elated: “For the first time since joining the Legion, I was by myself and dependent on my own intelligence, knowledge and initiative.”

The stranger in the strange land of 110-degree nighttime temperatures was able to sustain his freedom for half a week. He was quickly captured, taken to a Legion headquarters at Djibouti and tossed into solitary confinement. Guards interrupted his solitariness every afternoon, forcing him to crawl around them in the afternoon sun. Another captured deserter had harsher treatment, “suspended by his hands from the branches of a willow tree. His feet barely touched the ground, which was only a half-bad thing,” because the man’s soles were in tatters after the guards had made him walk three miles, barefoot, across a beach of volcanic rock.

Deserters, the author realized, were essentially people who too late learned that they couldn’t take the boredom or the beatings. They joined up for romance, not rigor. Now they had run out of places to run away.

Jennings went back to the fold, but only briefly. His second desertion, from Corsica, was easier and permanent.

One month later, in 1986, he was at Knightsbridge Crown Court, sentenced to prison for nine months on 17 criminal counts of burglary and deception. Later, for having helped save the life of another prisoner, Jennings earned a 14-day reprieve and soon went, like so many seekers, into the publishing business.

His book is an entertainment, larger than urban life, lustier than “Gunga Din” and longer than an hour of grisly brawling and gratuitous sex on television. The virtues of Christian Jennings? Presenting himself without dignity or disguise.

The morals of this madcap memoir? Escaping one’s past is no escape from one’s person. Boredom is possible anywhere on Earth. Authors come from everywhere.