Phelps partied with marijuana, a performance-detracting drug, and was suspended from swimming. Rodriguez took banned performance-enhancing drugs for three years and suffered no penalty but an uncomfortable television interview.

The American swimmer Phelps, 23, won a record eight gold medals at the Beijing Games last summer but lost an endorsement deal with U.S. food giant Kellogg Co after a British newspaper published a picture of the Olympic champion apparently smoking marijuana.

USA Swimming then suspended him for three months.

Rodriguez, 33, the highest paid player in baseball, admitted to ESPN television on Monday that he took a banned substance from 2001 to 2003 after Sports Illustrated reported he tested positive for testosterone and the anabolic steroid Primobolan in 2003.

He escapes sanctions from Major League baseball because it did not punish players at that time for using steroids.

"We should leave Michael Phelps alone. He's a kid. So he made a mistake. He owned up to it right away -- as opposed to A-Rod, whose been lying about it for a number of years," said Deborah Cohn, professor of marketing at New York's Touro College.

So far other sponsors have stood by Phelps, including Speedo swimwear, Omega watches, Visa Inc, Subway sandwiches and Hilton Hotels Corp.

FODDER FOR TABLOIDS

Rodriguez of the New York Yankees is on course to break the career home run record and his $27 million annual salary and stormy personal life have made "A-Rod," as he is known, fodder for tabloids.

So far none of his sponsors have announced they were cutting ties, though marketing specialists said he could still be dropped.

What would be worse to any baseball superstar, he may be denied entry into the sport's Hall of Fame after he retires.

Rodriguez lists apparel giant Nike, Rawlings sporting goods, baseball card-maker Topps and Oasys Mobile as "corporate partners" on his official website.

"If we freeze-frame right now, it would look like A-Rod got off pretty scot-free. But it's only two days old. It's got to affect his own endorsement possibilities," said Michael Josephson, founder and president of the Josephson Institute, which promotes ethical behavior in sports and society.

"People don't think horribly about swimming because one young swimmer smoked marijuana. It's different with A-Rod. The impact goes to the core of the integrity of the sport," he said. "Doesn't anybody have the moral strength to say 'No'?"

Rodriguez may pay when he plays in rival cities like Boston, where the fans are sure to jeer him with relish.