Magazine editors have long worried about encroachment of advertising onto the editorial pages, nowadays especially about advertising pages camouflaged as articles called "advertorials."

Now television is seeing a similar invasion, the long advertisement in program form, known as the "Infomercial.'I'd heard viewers express surprise that television would carry "shows" that are blatantly totally commercial and typically half an hour long, programs often dressed up in a talk-show or audience-participation format.

But so far you have to be a night owl to catch them, because they are shown after midnight. In the wee hours they are cheap, perhaps as little as $3,000 for a half hour in New York, $1,000 or less in Salt Lake City.

You'll find the infomercials listed in your television guide simply as "commercial program."

Because I'm not a night person I hadn't actually seen one until last week. That was after I heard some of their producers as panelists on the John McLaughlin program on CNBC, the cable's consumer news and business channel.

- ONE OF THE PRODUCERS said cynically, "All TV is commercial." (He also said the newspaper exists solely for advertising. "If there's any news in it it's by accident.")

One infomercial that failed was on how to raise drug-free kids. It flopped, a McLaughlin guest said, because it was "too intelligent."

Others pitch such courses as how to stop smoking, lose weight, achieve unlimited success in 30 days, "light his fire," learn to play the piano overnight, or sell products such as household gadgets or a body cream to control cellulite.

They often feature a celebrity who may be paid up to a million dollars a year for appearing, people like E.G. Marshall, Erin Gray and John Denver.

One of the panelists was the chief executive officer of a company that makes $30 million a year selling a system for covering bald pates with strands attached to existing hair. This commercial featured testimonials from hair loss sufferers.

- THE BIGGEST DISTINCTION between infomercials and advertorials is that the aired infomercials often lack credibility, as the panelists were quick to admit. They said their trade organizations were cleaning up the industry, however, through codes and in meetings with the FCC and FTC.

They also said local stations should help police the ads. (KSL tells me the program manager reviews all the shows for suitability to the local audience, though it is manifestly impossible for him to check out all the claims.)

Both advertorials and infomercials are often not clearly enough labeled as ads.

A Rutgers professor argued that a logo ought to be shown throughout to let the viewer know that the infomercial is a sheer sales message. Actual disclosure is considerably short of that, but in the Salt Lake market, at least, the infomercials are preceded by a disclaimer in which the local station says the program is an ad and cautions that the station isn't endorsing the product.

IN THE MAGAZINES, the word advertorial itself usually isn't used. Generally "advertisement" or "special advertising supplement" is printed on each page, usually in tiny type. In its June issue, Utah Holiday did, however, use the word advertorial to label each of the three pages in a "health update" section, which was text ads for seven physicians, a dentist and a specialty hospital.

The American Society of Magazine Editors has been fighting advertorials for several years and has developed some guidelines for them. Chiefly, ASME wants the ads clearly labeled and confined to a format different from articles and other editorial content.

I like the U.S. News & World Report practice of including at the end of special advertising supplements a disclaimer to the effect that the reading material is a paid ad and that none of it was prepared by the regular editorial staff. This notice appeared, for example, in the Dec. 17 supplement on learning to ski, interspersed with display ads over 15 pages.

Advertisers are finding more novel ways to use the advertorial format. A recent innovation is a series of one-page articles the news magazines have been carrying for months called "Outdoor Escapes." Each is labeled a "special advertising feature" and deals with such recreation trips as back country skiing and freshwater fishing. You have to look carefully to learn that the ads on "how to have more fun outdoors" are a soft sell by Izuzu.

Of course the advertorial isn't the only oblique way advertisers try to get attention. One not very subtle example: In Omni magazine's November issue, an ad for cellular telephones on the magazine's third page was made visible through a window on the cover. The publisher defended the integrity of the cover because no ad appeared on the cover itself and no product name could be seen. But that argument failed to placate the two top editors. They quit, saying the cover should be sacrosanct.

Journalists know that clear lines should be maintained between news and opinion or advertising. As the "Columbia Journalism Review" said in its March issue, lamenting the trend away from that ideal, "From a reader's perspective, this confluence of advertising and editorial is confusing: Where does the sales pitch end? Where does the editor take over?" The line, it said, must be drawn by the media, not left up to the advertiser.