Today in San Francisco, at their annual convention, CBS affiliates will cross the next frontier in television news. The network will screen for them excerpts from the pilot edition of a new CBS magazine show, "West 57th," that premieres for a trial run of six weeks starting in August.

A bold, risky departure in news programming, the program has been kept under particularly heavy wraps, in part because those behind it are worried about the reaction of some CBS News old-timers to this new-style TV show, which uses the latest production and technological techniques to revitalize the format. It introduces its young cast of reporters with an opening segment reminiscent of "The Mod Squad."

"West 57th," named for the street on which CBS News is headquartered in New York, is the most talked-about new magazine show, but all three networks are trying to develop them for prime time. This is a pivotal, precarious moment for the networks -- news audiences are down and political attacks on network news, always a part of the media landscape, seem to be escalating. Once network managements didn't even expect the news to make money. Now they demand it. It's a new world.

NBC News is readying "American Almanac," with Roger Mudd, for an August premiere and a trial run as a monthly show in the fall. ABC News, with "20/20" a fairly solid success, is harboring a project called "Seven Days." Although its executive producer, the highly respected Jim Bellows, says, "It's sort of, to put it nicely, on the shelf," ABC News President Roone Arledge reportedly expects another magazine to rise from its ashes.

Why does every network want a news magazine in prime time? As Don Hewitt, executive producer of the television landmark "60 Minutes," says, "Nobody's ever asked me a question about television to which the answer was not money."

Hewitt once estimated that CBS made $70 million a year in clear profit from "60 Minutes," perhaps half a billion dollars over the past decade. "I have no reason to believe it's wrong," Hewitt says of the figure. Networks buy entertainment shows, but they produce the news. News lets them make money the old-fashioned way. They own it.

Last year, says one industry insider, CBS Records star Michael Jackson and "60 Minutes" supported CBS Inc., "more or less." The search for another Michael Jackson goes on. So does the search for another "60 Minutes." But as Hewitt points out, network economics are such that "West 57th" could make handsome profits even if it were much less the success than "60 Minutes" has been. "If it does even moderately well -- if it's not an 'I Love Lucy' but just a 'Petticoat Junction' -- it's going to make money for them," Hewitt says.

"A successful magazine show says, 'We're innovative and creative, and we can sell in prime time,' " notes one network news insider. A profit-producing prime-time news hour helps justify the huge expense of network news divisions and, thus, makes them less susceptible to cost-cutting swoops from the corporate mountaintops.

"In our justifications, we look very hard at that part of the picture," concedes Lawrence K. Grossman, president of NBC News. "When a magazine show does succeed, it can stay on forever, as opposed to successful entertainment programming that might last only three or four years. News shows are less expensive to produce, less expensive to develop. If you look upon the news operation as a big factory, the more programs you can have on the air that amortize that cost, the more efficient your business."

Grossman also says, "You can't go into prime time and not worry about ratings."

The charge being made by some industry insiders, including old hard-liners at CBS News itself, is that "West 57th" has been conceived in terms of grabbing an audience, and not just any audience, but the young, affluent, free-spending consumers that advertisers crave for keeping the vigil. It has been months since the revised "Seven Days" pilot was completed and there has been no word from on high. Observers at the other networks say Bellows, a man of estimable reputation, is being treated shabbily by the mercurial Arledge. Bellows, who helped make a hit of "Entertainment Tonight," says only, "I'm still trying to figure out television."

A copy of the third and most recent version of "Seven Days," made to air April 21, 1984, reveals it to be a week-in-review show with morbid preoccupations: an on-camera killing in Baton Rouge, mass murder, molested schoolboys, threats of violence against political candidates, child abuse, gory movies. Moderated blankly by Tom Jarriel and Kathleen Sullivan, the program seems Tabloid Television to the hilt, something a little raw even for ABC.

There is a mini-irony buried within it. Just before commercial breaks, data readouts appear on the screen, and at one break, the five highest-paid corporate executives of 1983 are listed. No. 4 is Thomas S. Murphy, chairman of Capital Cities Communications, with more than $6 million in salary, and No. 5 is Daniel B. Burke, president of Cap Cities, with nearly $4.5 million. Two months ago, Cap Cities took over ABC and Murphy became ABC's new chief executive officer.

Bellows says there was "a very good reaction" to the show by ABC executives who saw it but then "it just sort of disappeared." He thinks one problem was that as a review of the week, "Seven Days" could not be rerun later in the year, the way "60 Minutes" and "20/20" segments can be (last Sunday, "60 Minutes" repeated a segment from 1973). Since "Seven Days" would cost about the same as "60 Minutes" to produce, roughly $500,000 a week, but would have to be produced 52 weeks a year instead of 26, the network would stand to make much less profit from it.

"I look on 'Seven Days' as just sort of part of the learning process," Bellows says.

At NBC News, the biggest worry is skepticism when it comes to "American Almanac." The network's track record on magazine shows isn't awesome: 10 failures in the last 10 tries. NBC affiliates, reeling with glee over the network's resurgence in prime time after seasons of humiliating defeat, will have to be carefully cajoled into accepting an iffy magazine show as part of the prime-time schedule. With that in mind, News president Grossman, recently installed vice president Timothy Russert, "Almanac" executive producer Edward Fouhy and host Mudd all made the pilgrimage to the network affiliates' convention in Los Angeles last month.

"We knew it would be the hardest sell at the convention," says Russert now. "The other news parts of the organization are doing well. Because of the history of news magazines at NBC, we knew a new one would be very tough to sell. That's why Roger and Ed came out there personally. It was a very conscious effort to neutralize resistance. We were somewhat successful, I think."

NBC affiliates don't have to worry about a yuppie show, apparently. Grossman says there is no overt or covert effort to "think young" aboard the old almanac of the air. "It's a disease," Grossman says of talk about luring young viewers. "I don't know how to 'think young.' Roger Mudd is not young. We still like to believe that if you put lively, vital, important stories on, you'll get an audience. I go crazy when people start giving me that stuff about carving up the audience into demographic groups."

For the record, Connie Chung, one of the reporters assigned to the program, is a youthful, and vivacious, 38.

Grossman insists that NBC Chairman Grant Tinker and NBC Entertainment President Brandon Tartikoff have been entirely supportive of the new magazine show, but they did not give it a weekly berth on the fall schedule. Instead it will air monthly, probably in a different time slot each time in order to discover where it might work best. Grossman is known to covet the 8 p.m. Monday slot, but that position is now occupied by "TV's Bloopers & Practical Jokes," a hit.

Grossman says he will not accept 10 p.m. on Fridays or Saturdays for the show; that's the dumping ground where NBC previously buried magazine programs. Will "American Almanac" ever be put opposite "60 Minutes" on Sunday nights? "No way," says Grossman. NBC made that mistake once before and was slaughtered. ABC and NBC sources love to point out that "60 Minutes" is in a so-called "protected" time period and that its enormous and lasting success is therefore somehow mitigated. FCC rules require that networks program either informational programming or children's programming in the extra hour of prime time, 7 to 8 o'clock, they get on Sundays. "60 Minutes" is also said to benefit heavily from football overruns during the NFL season.

The undisputed champion of network magazine producers, Hewitt of "60 Minutes," dismisses the "protected time period" talk: "I've never argued about that. That's the hand of God touching me. We're a freak occurrence; I admit it. Everything just caught on right -- the people, the time slot, everything. On the other hand, I'm not sure all those other shows would have done well in that 'protected' time period at all. Come to think of it, NBC had a chance and failed. NBC went to the well and never brought back any water."

Neither Stringer nor Lack would ever say so, but there has to be some feeling at CBS News that if "West 57th" succeeds, it can move in to replace "60 Minutes" when -- if -- it dies. Hewitt says simply, "I don't hear much about 'West 57th,' " and doesn't care much about it, either.

The golden age of "60 Minutes" may be over. Electronic Media magazine reports that its season average rating eroded from a 27.8 in the 1980-81 season to 22.2 for the season that just ended. The program, and its gallery of correspondents, are beginning to look old and a tad tattered. That's one reason Diane Sawyer was brought in.

Hewitt is not exactly biting his nails about eroding Nielsens. "Well, part of the glitz wears off," he says. "The big success of this show was, we brought people to the TV set who never would have turned it on at 7 o'clock on a Sunday night. But I think maybe the day is over when people would say, 'We've got to get home by 7 to see '60 Minutes.' It's just normal attrition. I would hope we'd stay in the top 10 forever, but maybe we won't stay in the top four or five. Listen, even Coca-Cola changed."

Lack, meanwhile, is imbued with the fervor of the pioneer and the Young Turk. "I'm thrilled," he says. "We're walking around slapping ourselves -- 'Is this true?' It's as if your English teacher came in and said, 'This semester, just read the books you want to read.' " Not that he's unaware of the ferocious internal political pressures that swirl around the program, and the pressure to bring it off.

"Every time the news division goes to Gene Jankowski and says, 'Let us try again,' that requires a tremendous commitment on everybody's part," Lack says. "You want to fulfil that commitment. You want to come through. You want to make them glad they gave you that chance." He pauses. "This will be my swan song, I think, if I can't get it right."