Jewel smuggler's trail of suspense; Green River high, by Duncan Kyle. New York: St. Martin's. $10

Fans of Duncan Kyle who shivered their way through "A Cage of Ice" and "Whiteout!" may warm to the knowledge that the British author has forsaken ice and snow for steamy tropical jungle in his latest adventure, "Green River High."

George Tunnicliffe Jr. is a rather misogynistic ex-soldier trapped in a boring job in a London bank. He has the misfortune to stumble upon several chaps who are in the process of robbing the bank, and he takes them on single-handedly. The resulting publicity brings him to the attention of two characters from his deceased father's past, who reveal that peculiar circumstances surrounded the senior George Tunnicliffe's fatal plane crash in the jungles of Borneo just after World War II.

Miss Charity Franklin is the ex-medical missionary who treated the dying flier and buried him in the jungle: She knows where the plane went down. J. C. H. Ludlam is a weasely fellow who was court-martialed for his part in a smuggling scheme he and George's father carried out: He knows that a fortune in rubies may be concealed somewhere in that aircraft.

Although George is reluctant to become involved with either, he soon finds himself stuck with both, on a wild ride up a jungle river in country swarming with Indonesian guerrillas, hunting for a plane that crashed 30 years earlier.

Miss Franklin (as she prefers to be called) shares the story and the consequences of the adventure equally with George, much to his annoyance. She is an enigma to him: Just when he thinks he has fit her into one of his bitter stereotypes, she shatters it. Whether dealing with English killers on their trail or blowgun-toting Borneo tribesmen, Miss Franklin not only equals her unwilling partner but often outdoes him in sheer grit.

Author Kyle takes his time putting all the pieces in position for the game, but the pace picks up as hit men move in on George, and there is some fine suspense with a chilling outcome. But when the scene shifts to Borneo for the river journey, the suspense falters. There Kyle's characters sometimes seem to rush into the arms of danger out of stupidity rather than necessity, and confrontations with nature do not always fulfill their potential to advance the plot: After the most dramatic encounter with the jungle river, George and company are no worse off than before . . . and even their Thermos comes through the battering intact.

At his best, Kyle keeps the reader riveted, and he is at his best when his characters are being pursued. But without anyone dogging their trail, they have a tendency to sit down and relax -- and so does the suspense.

A final note: St. Martin's has done Kyle a disservice by resorting to hard-to-read, compressed type with drips and specks of ink that are as annoying to the reader as the clinging jungle leeches are to the characters in the story.