Athletes have been doing commercial endorsements since before the days of Burma Shave. But never has one class of jock so dominated the TV advertising landscape the way professional basketball players do today. Everywhere you look, another handsomely rewarded hoopster is hawking product. That situation will only intensify this week as NBC begins broadcasting the NBA finals. Some athletes fare better than others in the commercial climate. Charles Barkley of the Phoenix Suns, for instance, is an extremely effective spokesman for Nike whether the tone is humorous (going one-on-one with Godzilla) or serious (“I am not a role model. Just because I dunk a basketball doesn’t mean I should raise your kids”). On the other hand, Orlando’s Rookie of the Year, Shaquille O’Neal, has been a bust. He comes across as a menacing oaf in those Pepsi spots, and his Reebok campaign is a recurring nightmare. Other players who have been caught flat-footed in ads include Chicago’s Scottie Pippen (Nike) and Detroit’s Isiah Thomas (Minute Maid Orange Soda). Don’t blame the ballplayers. It’s up to the ad agencies to coax natural performances out of these fast-action heroes. Often they fail. Consider the up-and-down commercial career of Michael Jordan. Most of the Bulls star’s innumerable ad campaigns have been uninspired. But Jordan has also appeared in the best spot yet devised for NBA stars: his long-range shootout with Larry Bird for McDonald’s (“Off the expressway, over the river, off the billboard…nothing but net”). Conspicuously absent from this endorsement gold rush lately is Magic Johnson. The former Laker was once Madison Avenue’s favorite son. But since his HIV announcement, admen won’t touch him with Manute Bol, Shawn Bradley or any other nearly eight-foot pole.