Tab, Mr. Dyson said, has been positioned as a diet drink. Diet Coke (and the company is not capitalizing the D) is being positioned as a good-tasting cola that incidentally is low-calorie.

Of course, Coke's ostensibly big news is a switch from recent industry pronouncements from the second-string competitors, Seven-Up and Pepsi-Cola, both of which have come in with caffeine-free colas. Pepsi's announcement came as recently as Wednesday.

Asked about his own company's intentions in the no-caffeine arena, Mr. Dyson responded that when Coke believes the time is right it will be there with such a product.

Might he use the name Tab, as rumor has it? That is certainly one of the company's options, he said. Although diet Coke is being sweetened with saccharin, the company's president said he did not rule out switching to either the new aspartame or cyclamates.

Part of the advertising news here is that the campaign is not being done by Coca-Cola's regular agency, McCann-Erickson, but is handled instead by SSC& B, another of the Interpublic Group of Companies that, if Coke had its way, would still be secretly doing TV advertising for its Mello Yello beverage while McDonald & Little, Atlanta, continued as the publicly acknowledged agency of record.