"Persuading yourself or anyone else to start running is seldom easy," concedes writer-runner Jim Fixx.

"Most of us want to be healthy, feel good, look young and live a long time. But the mind is ingeniously inventive at devising excuses."

Part of the inertia problem "is that too many of us were taught to look on exercise as punishment." Also, people often feel the "preventative medical benefits of exercise are for the other guy. And the problem is often compounded by the fact that exercise isn't all fun at the beginning."

In his "Second Book of Running" (Random House, 240 pages, $10), Fixx sees motivation as an individual matter. Some runners are motivated by losing weight, some by getting lower life insurance premiums and others (himself included) because it's fun.

Some of his weapons in "the war against sloth:"

Understand what exercise does. "When you're pushing soggily along . . . it helps to know exactly what you're accomplishing." Reading about the physiological, biochemical and personality chages that occur with endurance conditioning will make it easier to make the necessary life style changes.

Make a mental commitment. If you take promises seriously, this may be all that's required. When your enthusaiam wanes, dedicate a run to the memory of someone you've cared deeply about.

Identify your own stumbling blocks. Make an honest list of the reasons you find it difficult to run. Then try to overcome each objection. If your reason is hating to get up early, run in the evening instead, or go to bed earlier.

Acknowledge running's disadvantages. Those who were promised "painless, instantaneous miracles, become discouraged when they find that much of the time it's just plain hard work." To overcome discomforts, reward yourself afterwards with something pleasurable. Or punish yourself by writing checks to organizations you hate (he mentions the Ku Klux Klan or American Nazi Party) and mail them if you fail to meet your running goal.

Set goals, then periodically evaluate your progress. Fitness-testing can be invaluable inspiration for those who discover they've lowered their heart rate, lost weight and increased cardiorespiratory reserves.

Insist on making time for running. Start workouts at a certain time every day and accept them as a part of your regular schedule.

Run with others. Beginning runners, in particular, might benefit from running with one of the area's many running clubs to gain inspiration and to increase self-discipline.