It has been a bleak summer for Bill Rodgers. Just when everyone began believing that he was the king of the road, threats to the throne began cropping up.

In Denver in July, he was beaten by Frank Shorter in a 10,000 meter race. Two weeks later, at a 10 miler in Milwaukee, he was again beaten by Shorter, who set a United States record of 47:34. At Falmouth, Mass., in mid-August, Rodgers finished third. He had won there three times before and held the course record. No more. The current champion and new record holder is Craig Virgin. In a marathon in Montreal, Rodgers finished a weak 15th.

I think I know the trouble. Rogers has become a limousine runner. Last May, he came to Washington to be celebrated by the Congress and the White House for his victory the month before in Boston. After lunching with some senators and representatives, Rodgers was taken to see Tip O'Neill. The pair bantered in the speaker's office for about 10 minutes.

When Rodgers was leaving, O'Neill called out to his chaffeur: "Get the limousine and take Mr. Rodgers wherever he wants to go."

Rodgers' face lit up with one of those golly-gee-whiz expressions that he uses in happy moments. There he was, just an ordinary guy who hit a hot steak and now he was being attended to by The Great Tip.

When the car pulled up under the dome of the Capitol, the chaffeur sprang out to open the door for Rodgers. The back seats in the long, low and black limo were billowy in cushioned-softness. Rodgers sank into them, his frail frame almost swallowed up in the seat that was accustomed to the immensity of Tip O'Neill. The car and its suddenly precious cargo sped off -- to a tuxedo shop, no less, for Rodgers to rent an outfit for a presidential dinner that night.

That doesn't look good, I thought to myself on seeing it all. Celebrityhood is bad business for athletes. It is different than fame, which comes as the result of accomplishment. No compromises with the world are necessary.

But to be a celeb means that the athlete has to wink at a few things, change the way he thinks of himself and allow the good intentions of others to share space in his heart with his own goals. O'Neill meant well in ordering up the chaffeur, but Rodgers should have said no thanks, a cab was good enough to bring me here and it is good enough to take me away.

By this time, though, Rodgers had already gone so far along with the celeb routine that perhaps it didn't much matter. The audlation of the congressmen during lunch felt good. Being at Jimmy Carter's table for dinner would feel better.

We have no way of knowing whether Rodgers' defeats this summer are linked with his victories off the road, especially since he's never been known as a warm-weather runner. In June, he flew off to France for a week of frolic under the merry guidance of Perrier. The company jetted Rodgers to Paris with a group of runners whose names had been picked out of hats in Perrier races around the country. This was a "Run With Bill" trip. Some people who were asked to go along declined.

I don't imagine Rodgers had a choice. He is a Perrier runner who must go along with the public relations directives of the company.

This is proper and fitting. But it isn't concentrating Rodgers' attention on what he does best, running.

We will know more this fall at the New York and Fukuoka marathons whether the limos, trips to France and other diversions of the celeb game are dulling Rodgers' edge. Few athletes are able to resist the lures. It is human enough to think that after all the years of slaving to get to the top that it is natural to enjoy a perk or two.

Except that something is lost. I have always thought that Arnold Palmer would have lasted much longer as a championship golfer if he hadn't gone commercial so soon. Now it is happening to Jack Nicklaus, who, in his own admission, spends half his time on business deals.

Rodgers is well short of going this far. It may well be, too, that his poor showing this summer are the inevitable letdowns from his incredible string of wins the year before.

But Rodgers is pressing himself to win the marathon in the 1980 Olympics. He knows that he isn't the best in the world until he takes a gold medal.

And now, with Frank Shorter coming back from his foot injury and settings records once again, even more pressure is felt. There is someone who has been there and now he wants it again. With only three spots open for the United States marathon team, Rodgers might do better to train just to make the team and leave the big day in Moscow for later.

No formula exists by which an athlete can judge when he or she has crossed the line between fame and celebrityhood. It is the most personal of feelings, having to do with intangibles like intensity and purity. For top runners like Rodgers, who train more fanatically than nearly all other athletes -- 15, 17, 20 miles a day for almost every day of the year -- the difference is perfection and mere greatness can be a matter of seconds in a 10-mile race.

Rodgers has lost some of those seconds this past summer. If the limos have turned him soft, he had better get back to hailing cabs. Or maybe even walking, the way some hungry scrapper is now doing as he thinks about making the marathon team for Moscow.