At a time when television is under pressure to reduce violence, four major pay-TV channels are instituting a labeling system to warn viewers about the content of every program they offer--but not only with regard to mayhem. The advisories also will cover nudity, sex and language.

Cable executives deny that the move is in response to congressional pressure and say it will not affect what gets programmed on HBO, Showtime, the Movie Channel and Cinemax. Nor will movies or programs be edited, bleeped or altered in any way to change the rating.

They describe it as a voluntary effort to provide more information to their subscribers, especially to parents trying to limit their children's exposure to violence, sex and offensive language.

The standardized, 10-category advisory system will go into effect Friday on HBO and Cinemax (which are jointly owned) and later this month on Showtime and the Movie Channel (which also are jointly owned).

"I think that because the concern over violence on television is occurring simultaneously, this could be perceived as a reaction to it," said McAdory Lipscomb, executive vice president of Showtime. "If we had not been providing advisories for years, it could be construed that way. But the thought is simply that, with so many images coming across our television screens today, better information about those images is needed."

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Sen. Paul Simon (D-Ill.), who has led the crusade to pressure television executives to reduce violence on TV without direct government involvement, believes "it is helpful to provide viewers with more information about what is on television, especially for parents trying to guide their children's viewing habits," a spokesman said. "But labeling is no substitute for a general reduction in glamorized violence."

He added that Simon will continue to focus on monitoring what actually gets shown on TV in an effort to limit the amount of violence. Simon has no intention of lobbying other broadcasters or cable channels to adopt a similar advisory system, nor would he frown on its implementation elsewhere, the spokesman said.

Under the pay networks' new ratings system, there are four categories of violence: mild (MV), violent (V) and graphic (GV), with a separate category for rape (RP), because the companies have heard from their subscribers over the years that sexual violence is particularly offensive to some viewers.

Sex is divided into three categories: brief nudity (BN), nudity (N) and strong sexual content (SC).