Indoor track has always had the feeling of a large family gathering, especially in the days when the old Madison Square Garden on 50th Street served as the homestead. Thousands packed the place weekly to celebrate the joy of the sport and exchange the endless esoteric data peculiar to it. Everyone jammed together in the dead of winter for the warmest of times.

A modern-day variation occurred yesterday at George Mason University when 5,000 crammed into a modern field house for a look at some of the world's most famous runners circling one of the world's fastest tracks. Two of the most famous couldn't stay away, succumbing easily to the twin temptation of both competing and then watching the current world-class athletes with the rest of the audience at the eighth annual Mobil Invitational Track and Field Meet.

Frank Shorter, 1972 Olympic marathon champion, and Bill Rodgers, winner of four Boston and four New York marathons, hooked up in a masters' mile that neither expected to win -- and didn't. They're both 47 and were just happy to be around a gathering of colleagues. "It's fun to come to a track meet," said Shorter. "I came to see the other athletes."

Actually, Shorter and Rodgers happily obliged the race's sponsors to join area competitors, who had the opportunity to be heroes to their families and friends. After winning in 4:35.53, Chuck Moeser of Herndon found himself in a media room standing between Shorter and Rodgers.

"Will somebody please take this picture and send it to me?" Moeser begged. "Pinch me. This has got to be too much fun."

Moeser, the father of four, is in the remodeling business -- his company is aptly named Running Construction. Kiddingly, Shorter attributed Moeser's victory in part to his age. He's a mere 43.

"There's a big difference between 47 and 43," Shorter insisted.

Shorter, who lives in Boulder, Colo., and whose name is synonymous with the marathon, had not run an indoor race since the 1987 Millrose Games masters mile. But he found it far too appealing an offer to pass up -- an airline ticket and modest appearance fee -- to mix with hundreds of track buffs he knew and run against his friend Rodgers.

"Bill and I just don't compete against each other that often," he said. Shorter feigned envy that Rodgers is like a machine, always ticking, remaining almost injury free despite the passing years, whereas last spring Shorter broke his ankle -- just the latest in a career that's periodically included such setbacks.

"I had to take the summer off," he said. "I decided to experiment with some weight training. I'm 10 pounds heavier." He still looked like a rod beneath his mop of graying hair; he stands 5 feet 11 and now weighs all of 145 pounds.

"If I'm going to be slow," he said, "I may as well look fairly decent."

More seriously, Shorter stressed that young athletes should not even consider the marathon until "they're into their 20s." And Rodgers, who lives near Boston, echoed the theme that seeking enjoyment in sport rather than often elusive riches can be more satisfying. "It's always better to concentrate on your specialty when you're younger," he said. "Find a sport you like and concentrate on that."

Fun is what both Shorter and Rodgers had yesterday. "When Chuck went by, I wanted to say, Get going,' but I couldn't get it out," Shorter said.

For the record, Rodgers finished fourth in 4:43.22. Shorter was 14th and last in 4:59.67. But the feeling at George Mason was that it was great seeing them, and they spent the rest of the afternoon renewing acquaintances. It was just like old times on the indoor track circuit. CAPTION: And they're off in the masters' mile. From left to right, Chuck Moeser, Paul Peterson, Frank Shorter and Bill Rodgers. Herndon's Moeser was first with a time of 4 minutes 35 seconds.