Before making any wisecracks about the elderly gentleman running past in Rock Creek Park, it might help for you to be sure you can beat him in a race. For at 70 years of age, Paul Fairbank isn't ready for any youngster to commit him to a rocking chair.

"If anybody says anything, I just say, 'Put on your running shoes and let's run,'" stated the 5-foot-7, 128 pound resident of Cedar Lane in Bethesda. "I'm convinced man was made to run for his dinner."

Fairbank didn't start running until the age of 62, shortly after his retirement from a career of quasi-legal government work. "I had no idea people [WORD ILLEGIBLE] ran until I read Dr. (Ken) Cooper's book Aerobics (a detailed description of how and why to run)," said the retired member of the Maryland bar. "I read the book March 1, 1963, and it made such an impression on me, I started running the next day."

Eight years later, Fairbank rates as a national class age group runner. He has competed in distances ranging from one mile to a marathon (26 miles, 385 yards). His 12:36 clocking for 3,000 meters (1.8 miles) in a Sept. 25, 1976, race at the Tidal Basin set a national 69-year-old age group record. He also holds the record for 70-years-old with 12:50.

Fairbank's greatest attention, however, came on an occasion when he wasn't running against the clock. On inauguration Day, he donned his yellow Potomac Valley Seniors sweatsuit and ran on a treadmill in the parade on the float for the President's Council on Physical Fitness and Sports.

"It wasn't even a workout," explained a smiling Fairbank of his hour-long job. "I had the thing turned on high and I couldn't even get the thing going fast enough."

"I felt good that day," he continued. "I waved at everybody. I waved at the President. It was a bird's eye view, a front-row seat. I would have almost paid to do that."

Fairbank enjoys the camaraderie of runners and the good health that accompanies the exercise. "This is one of the best things I've ever done," remarked the 1929 alumnus of Loyola Baltimore) College and 1939 graduate of University of Baltimore law school. "It made me really happy. And the men you meet; they're wholesome and they have a lot in common. It's very satisfying. You meet all the young runners and they make a big deal out of it, especially in the marathons."

Despite his success, Fairbank has trouble talking his cronies into joining him on his jaunts through the park. "I've given up trying to talk to my contemporaries. They're just deaf," commented Fairbank, who has lived alone since being divorced in 1947. "They don't hear you. Or they just change the subject. I've been to the doctor, he listens to my heart and says I'm in real good shape. I wish I could get some of them to run."

In between recording 40 to 60 miles per week, Fairbank can be found amusing himself with a number of activities. He enjoys doing maintenance on his cabin cruiser, fishing, bicycling, playing with his ham radio and traveling around the country in his house trailer.

Fairbank visits the Florida Keys - his favorite running spot - whenever he can. The grandfather of three has made a pair of lengthy trailering trips through Mexico, reaching as far as Guatemala.When he gets tired of driving, Fairbank will pull into the nearest park and run for an hour - six or seven miles to loosen himself up before returning to the wheel.

Fairbank prides himself on having "read all the mysteries on the market." He combs through libraries for mystery books with his friend Jack O'Connell, 65, of Chevy Chase. But his pal "disapproves of me running" and refuses to join the daily workouts.

Fairbank, who plans to run in an international masters (over 40) competition in Sweden in August, would still like to break six minutes (he's run 6:10) in the mile and set some new national age-group records. He would also like to chop 30 minutes off his three hours, 58 minutes time in last December's Maryland Marathon.

And on Feb. 26, Fairbank departed for St. Paul, Minn., for a month's training for a new career."I'm going to learn to make doughnuts," explained Fairbank, who plans to open a summer Mr. Donut franchise this year with his daughter and son-in-law in Ocean City. "It'll take me a month to learn."