Pedestrian in Borneo : STRANGER IN THE FOREST On Foot Across Borneo<i> by Eric Hansen (Houghton Mifflin: $17.95; 286 pp.) </i>

The fantasy must occur to every Westerner who ventures even a few miles into the thick jungles of Borneo. What if you wandered off, got lost in there and were suddenly alone? What would happen to you? Who would you see? How long would you . . . survive?

Tommy Ngang, the native guide who led me and two companions to the Gulu Caves in Sarawak last fall, laughed when I raised those questions.

“You might last one week,� he said, holding up an index finger.

What would get me, I wondered. Animals? Headhunters? Malaria? I had already been told that the No. 1 killer of man in the Borneo jungle was the falling tree branch. Did the odds really favor my being fatally conked within seven days?

“You would probably die from poison,� Ngang said. “You would get hungry and you would eat something you shouldn’t.�

Judging by the experiences relayed in Eric Hansen’s “Stranger in the Forest,� being poisoned is a daunting prospect for even experienced adventurers. Hansen, whose biographical data recalls his stints as a fish smuggler and wild dog hunter, had guides save him several times from dining on lethal vegetation in the wilds of Borneo.

In 1982, Hansen set out on a journey that possibly only he had ever imagined. For years, he had wanted to cross the Borneo rain forest on foot, some 300 miles (as the hornbill flies) from the last navigable tributary out of Miri in northern Sarawak to the coast of Kalimantan in Indonesia. There was no record of any such previous schlep, and Hansen had been unable to locate a single native who knew the entire route.

When he started out, Hansen had only a basket of barter goods, some Malaysian money and a useless 40-year-old map. Seven months, several guides and 1,500 miles later, he had not only gotten safely through the forest but had turned around and come back.

There were encounters with wild boar, snakes, leeches and poison caterpillars. He traveled with nomads and learned to live off the land. He saw corners of the planet that perhaps no Western man had ever seen.

Unfortunately, reading Hansen’s account of all this takes almost as much determination as the trip itself. He is a game adventurer, but he is no storyteller. The events are laid out in dull, dispassionate chronological detail, with missed dramatic opportunities buried in almost every paragraph.

Hansen wasn’t even able to make himself an interesting, sympathetic narrator. He manages to cram both the essence of his childhood and the evolution of his adult persona into a two-page introduction, and though we spend seven intense months with him, we come away knowing virtually nothing about his life outside the jungle.

Finally, it is hard to like a person who, out of self-interest, smuggles shotgun shells into the jungle, to be used as barter for whatever he needs, and continues to hand out shells even after realizing that his guides cannot resist blasting away at almost every animal they see.

One thing a visitor learns soon after arriving in Sarawak is that the graceful rhinoceros hornbill, the symbol of native culture, is nearly extinct. Yet, when Hansen was asked by a guide if he’d like to try one for lunch, he said, “Yes, certainly.�

The guide then loaded one of Hansen’s contraband shells into his homemade shotgun and blew one of the gorgeous black and white creatures out of a tree. A few more fascinated visitors like him and the jungles of Borneo won’t be quite so fascinating, to Hansen or anyone else.