He subjected that lithe body and those legendary legs to a 15-kilometer (9.3 miles) run yesterday in the heat of Jacksonville, Fla., despite a cold that has nagged him all week.

He won that race with a clocking of 44:46. And then, he put himself at the mercy of the airlines - "my toughest competition," he said with mock solemnity - to fly to Washington later yesterday for a few hours rest before lining up this morning to run 10 more miles in the sixth annual Cherry Blossom Classic.

"Why do I do it?" asked Bill Rodgers, America's premier long-distance runner and one of his sport's most eloquent spokesman. "Very simply, I live to run, and I love to race. I'm also told Washington is a lovely place to be this time of year."

There are 3,400 other men and women who apparently feel the same way. Cherry Blossom race organizers accepted that number of entrants - 1,000 more than they had originally planned - and the thundering herd will set off from the Ohio Drive start (and finish) at 8:30 a.m.

Rodgers will be at the head of the pack with a number of other runners who have gone 10 miles in under 52 minutes, and he will have plenty of competition over a fast, flat course that winds down Ohio Drive, into East Potomac Park and around Hains Point and the Tidal Basin.

There are three former champions in the field: Dan Rincon of College Park, last year's winner in 49 minutes 44 seconds; Carl Hatfield of Phillippi, W. Va., a two time winner who holds the course record of 49:09 and Jack Mahurin of Springfield, Mass., the 1974 champion.

A number of outstanding women also are entered, including Julie Shea, a freshman at North Carolina State. Shea set a national record of 56:08 as the first woman finisher in the Cherry Blossom last year.

Runners from 26 states and Canada, ranging in age from 75 to 8, are entered and Rodgers, the 30-year-old former school teacher turned shopkeeper - he sells running equipment, what else - is the favorite.

The climate conditions - cloudy skies the temperatures in the high 50s - will be ideal for Rodgers, who says "the cooler the better" for his last hard run until the Boston Marathon April 17.

"I'm probably pushing it by doubling this weekend," Rodgers said over the telephone earlier in the week, "but I think I know enough about myself to get away without getting injured. Yes, it's a gamble, but a good one."

Rodgers says he had been averaging only 110 to 120 miles of training each of the last three weeks because of a hectic travel and race schedule. "It's very poor, really," he said. "I should be higher, but I'm counting on my miles in the bank to get me through in Washington."

The next two weeks will be spent in thorough preparation for the Boston Marathon, and a confrontation with his good friend, Frank Shorter, who is making a comeback after an ankle injury a year ago.

Rodgers won in Boston in 1975, breaking Shorter's American record for the marathon by 35 seconds with a clocking of 2 hours 9 minutes 55 seconds, an average of 4:57.3 per mile.

Life has been a joy for Rodgers ever since. "Before that race, I was living in poverty, and now I'm not," he says. "It helped me get a job teaching. Suddenly, people were calling and asking me to come to their races, and now I've got the store. I'm dependent on no one except myself, and it's made it much easier to train."

He is also delighted about America's latest running boom, and not only because it's good for business at his Chestnut Hill Avenue shop three miles from the Boston Marathon finish line.

"I'm sure there are a certain percentage of people who will drop off, and they're the ones who are in it because it's the latest fad," Rodgers said.