Everything to know on cycling; The Complete Book of Long-Distance and Competitive Cycling, by Tom Doughty, Ed Pavelka, and Barbara George. New York: Simon & Schuster. 380 pp. $17.95 in hard cover, $8.95 in paperback.

''Not only is the bicycle the most efficient use of human power ever devised, it's fun to ride.'' If you're inclined to agree, you're ready for ''The Complete Book of Long-Distance and Competitive Cycling.'' Its avowed aim is ''to take you, the enthusiastic but still developing rider, and help you grow into a cyclist capable of great feats.''

Even if you're not so enthusiastic to begin with, you're liable soon to be won over by the three authors - an Olympic racing cyclist, and the editor and publisher of a prominent cycling magazine. They cover their subject right down to the last spoke and sprocket, with expert advice on bicycle maintenance, planning a tour, training and feeding of riders, and much more.

Did you know that top cyclists allow their tires to age like cheeses before mounting them on their bikes? That ''shoes are the most important component you will ever buy, next to the (bicycle) frame itself''?

If you've resolved to get more exercise this spring, perhaps bicycling is the way to go. Age is no excuse - some competitive riders mentioned in the book are rolling well into their 80s.