Running fever has definitely reached popular fiction--but this wholesome, old-fashioned, likably corny novel offers more than racing heartbeats and straining tendons: McNab--the ""athletic consultant"" for Chariots of Fire--compounds his running expertise here with other sports (boxing, Highland Games), with 1931 atmosphere, with warm camaraderie. . . and with an appealing flim-flam man of a hero. This is veteran promoter/con-man Flanagan, mastermind of the ""Trans-America"" race: 2000 marathoners will attempt to run from L.A. to N.Y., averaging 50 miles a day for three months, with $300,000 in prizes for those with the best accumulated times. Flanagan's profit? The $200-per-runner entry fees, the film rights, and the fees paid by towns across the country-for the privilege of being put on the runners' route. Among the contestants: 54-year-old ""Doc"" Cole, a sometime snake-oil peddler and longtime expert-runner; Hugh McPhail from Scotland, a Depression victim; ex-steelworker Mike Morgan, wanted on a manslaughter charge; desperate for money to send home to his motherless son; Juan Martinez, hoping to save his native Mexican village; an English nobleman; a group of Nazi youths (complete with drug-dispensing manager); and ex-burlesque dancer Kate Sheridan, who'll get a special prize if she comes in among the top 200 finishers. Predictably, then, much of McNab's attention goes to these featured runners' aches and pains through desert and mountain country--convincingly detailed. Not so predictable are the offbeat detours along the way: sabotage, deals and bets, Highland flings in McPhee, Utah, a tad of romance. But the emotional heart of the novel is the intra-runner fellowship: mutual assistance, prize-splitting agreements--plus some vengeance when Martinez is killed in Chicago by Capone henchmen. And before the windup--an unexpected, winner-takes-all one-day marathon in N.Y.--there'll be amusing involvements with a famed evangelist, the FBI, and a foul, stuffy Olympics official who is determined to destroy Flanagan's vulgar, carnival-style event. Episodic, contrived, and not always plausible? The easygoing pleasure, however, is steady throughout.