The late radio comic, Fred Allen, once sourly said of TV's impact: "The next generation will have eyes as big as cantaloupes - and no brains at all."

Two generations later, the eyes remain normal, the brains more or less intact. But what would Allen say of the impact of cable and its flood of viewing choices?It's not going to let up. This year, at least 15 new cable channels hope to start, according to the National Cable Television Association, which estimates that the average cable system has 35 channels.

Some newcomers won't leave the gate. Those who insist they will - despite the recession, scarcity of channels on cable systems and cable operators' worries about re-regulation of cable - include:

- The Courtroom Television Network, a merger of two previously proposed channels. Offering live and taped coverage of American trials, legal news and commentary, its partners are well-heeled - Time Warner, Inc., NBC and Cablevision Systems Corp.

- The Sci-Fi Channel, whose advisers include Gene Roddenberry of "Star Trek" renown. The channel's president, Mitchell Rubenstein, says Sci-Fi will offer a 24-hour mix of science fiction, "science fact," fantasy and non-violent horror programming, including the original "Dark Shadows" series.

- The Cowboy TV Network. President Mack Long promises western movies, original programming and music - gospel and blues as well as country - despite the much-publicized tax woes of his best-known pardner, Willie Nelson.

Other hopefuls range from the Christian Science Monitor's The Monitor Channel to Celticvision, aimed at the nation's Irish-Americans but based in the distinctly non-Hibernian hamlet of Beverly Hills, Calif.

How many will succeed? "That's a tough call," says Audrey Steele, associate media director of the Saaatchi & Saatchi advertising agency.

The consensus, she says, seems that "this is a terrible time, although is there ever really a good time?"

She notes that some previous newcomers defied the odds, notably The Discovery Channel, launched in 1985 and now seen in 57 percent of the nation's 93.1 million TV households.

"They said it would never make it. But of any time to choose to launch a network, I would say this is probably the worst, with the (poor) economy."

"It's a difficult time," says Discovery chairman John Hendricks, whose non-fiction documentary service began with only 150,000 subscribers.

"The biggest factor is the settlement of the re-regulation issue," he says, referring to congressional proposals to put new controls on the largely unregulated cable industry and the rates cable systems charge subscribers.

Such proposed legislation died in the last Congress - approved by the House but expiring in the Senate under the threat of a White House veto.

It recently was revived by Sen. Albert Gore Jr., D-Tenn., and two other senators. "Cable television customers are being gouged and current law tells the cable companies that it's OK to be a thief," Gore said.

Hendricks is optimistic that the proposals will die again, thus freeing capital to both increase channel capacity - cable operators call that a "rebuild" - and to help cable operators buy new program services.

But if "they're held to some kind of artificial (subscriber fee) increase imposed on them by some regulatory agency, that's the doom of new services." Analyst Larry Gerbrandt of Paul Kagan Associates in Carmel, Calif., says he doesn't think "the economy or reregulation are directly tied into it."

"I think it's more of an issue in which cable operators are holding off on rebuilds for a period . . . which slows down expansion of channel capacity."

He says the situation is eased slightly by the decision of Time Warner and Viacom to merge their two new existing comedy channels, The Comedy Channel and Ha! The TV Comedy Network, into one called Comedy TV early this year.

Even in lean times, cable operators usually add one or more new services a year, he says. But that's only after a long, hard look at a new network's wares and prospects for success.

"The industry puts you through a gantlet," he says. "They want you to be out there for 18 to 24 months, to see what you have to offer at three or four major cable (industry) shows.

"And as channels open up, only those with staying power, the financial backing, survive . . . it's a natural selection process where only the strong survive the gantlet."

Despite that, both he and Hendricks think the scarcity of channels may soon be a thing of the past, thanks to new technology like fiber optics and "bandwith compression" that will allow many more channels on a system.

Some relatively new systems, like one serving the New York City boroughs of Queens and Brooklyn, have 76 channels.

But Hendricks can see as many as 200 channels in the future, many devoted to what he calls "sub-niche" programming - the TV equivalent of magazines devoted to single subjects like golf, yachting, tennis and photography.

"We have only scratched the surface," says Gerbrandt. With new pay-per-view and interactive channels, and what he calls an "explosion" of single-subject subscription channels in the wings, "within five years we'll be talking about hundreds of channels."

In the meantime, new-network entrepreneurs like Sci-Fi's Rubenstein remain full of optimism about cable as it now exists, both for advertising support and opportunities for growth.

From his headquarters in Boca Raton, Fla., Rubenstein said his advertiser-supported service will start this summer with more than five million subscribers.

He predicted that it will reach its break-even point of between 16 million and 20 million homes within three years, possibly earlier.