NEW YORK — The cable industry is crowing about the flood of new viewers that sampled primetime programming on basic cable during the first 11 days of the May sweeps, despite the almost nightly parade of powerhouse events on the broadcast networks.“It’s as though the broadcast industry invited people to a huge banquet, but they ended up going next door to eat off cable’s buffet,” says Jon Sims, VP of research for the Cabletelevision Advertising Bureau. Sims is referring to Nielsen numbers which show that 2 million more households were watching basic cable networks, as a category, in primetime during the period of April 24 through May 4, compared with the similar period a year ago. By contrast, the Big Four broadcast networks have lost a total of 440,000 households in the year-to-year sweep comparisons. An avalanche of broadcast promotion — for everything from the hourlong I-am-gay “Ellen” special episode to miniseries such as “Robin Cook’s Invasion” and “Stephen King’s The Shining” to theatricals “Forrest Gump,” “The Mask” and “Ace Ventura, Pet Detective” — has propelled massive numbers of new cable subscribers to turn on their TV sets since April 24, Sims said. “But the ratings show that these people are not staying with the broadcasters, but instead surfing around the dial and finding that cable offers them a hell of a lot of extra choices,” he added. And the May sweeps stand out in particular because cable decided not to play dead, as it has done during past sweeps periods, frightened off by the broadcast-network blockbusters. For example, while TNT and TBS were making hay with National Basketball Assn. playoff games and ESPN with Stanley Cup hockey games, A&E was running the six-hour BBC adaptation of “Ivanhoe,” E! was digging into the life of singer Karen Carpenter in a two-hour documentary special and USA was scheduling primetime movies “Jennifer 8″ and “American Gigolo.” But one broadcast-research executive, who requested anonymity, said that in the key demographic category of adults 18 to 49, which advertisers pay top dollar to reach, the ratings are up slightly for the Big Four in the May sweeps. And at least some of cable’s pickup in the number of viewers is traceable to the addition of new networks and the fast subscriber growth of midsize networks such as ESPN2, History Channel, Learning Channel, Sci-Fi Channel and Cartoon Network, the executive said. He added that, individually, the mass-circulation cable networks such as USA, ESPN, TNT and Discovery have not shown any appreciable increases in ratings over the past few years. That’s an indication, he concluded, that although cable still is continuing to cannibalize the broadcasters, it’s also beginning to cannibalize itself.