The memo from executive producer John Sacret Young to the cast and crew of ABC's "China Beach" was cheerfully glum, if such a thing is possible.

"In all this I sometimes wonder why we struggle but I'm attaching two letters we received yesterday. They make it all worthwhile," it said.The acclaimed creator of one of television's most innovative shows now knows firsthand the ultimate rule of iconoclastic TV making:

Fan mail, rave reviews, loyal audiences, Emmy awards and just plain talent are not enough. A television show lives by the A.C. Nielsen Co. ratings. And dies by the ratings.

"China Beach" still has a pulse, but it's in a coma. NBC's "Parenthood," another highly acclaimed but little-watched program, is likewise in limbo.

Their predicament is nothing new in the world of television, where quality and success quite often are mutually exclusive.

What is new is the lengths to which some producers will go to pressure a network into standing by a dismally rated, but quality-minded, show.

In the face of threatened cancellation, people like Young and Andrew Susskind of "Parenthood" are talking back to networks that have the power to make them and their staffs eligible for unemployment.

"I think they're caught in real short-term thinking right now," Susskind said of NBC. "They're No. 1, but their lead is shrinking. I'm not sure they have the same kind of confidence they had when they were No. 3 and shooting for No. 1 - which was to give quality shows a chance."

"The sad part is that, overall, ABC has supported the show the way you support someone you love and then shoot off another limb," Young said of "China Beach."

The Fox Broadcasting Co. gave probably the biggest chance of any network to its highest quality series.

"The Tracey Ullman Show" - which spawned "The Simpsons," won Fox its first Emmy and ran for four seasons - was often the least-watched show on television. Still, Fox never yanked it. It ended this year only after Ullman quit.

NBC will not say if "Parenthood" will be canceled.

"They've said it's very iffy right now," said Susskind, the president of Imagine Television, which produces the show. "I'm doing what I can to at least let people know that the show is in trouble."

What Susskind is doing is a calculated effort to place pressure on NBC. By calling television critics who gave "Parenthood" favorable reviews and making himself available for interviews, Susskind is upping the cancellation game's ante.

Of some 30-plus new shows this season, "Parenthood" stood out for several reasons. It was produced by the television division of Ron Howard's highly successful Imagine Films, it was a take-off from the popular feature film of the same name, and it featured an ensemble cast that included Ed Begley Jr. ("St. Elsewhere"), Jayne Atkinson ("A Year in the Life") and William Windom (My World and Welcome to It").

It also got great reviews.

It didn't, however, get great ratings, a fact that Susskind blames in part on its time period of 7 p.m. Saturdays.

Susskind wants NBC to move the show and stick with it just a little longer. "Given the research we've done, any time period is better than the one we're in," he said. NBC executives declined comment.

Changing time periods is a common network maneuver for resuscitating dying shows. In most cases, though, it only prolongs the inevitable.

Young knows this well. "China Beach" has changed time slots two times in two years. Marked for cancellation last season, the award-winning Vietnam War series was saved at the last minute, only to be moved to the kiss-of-death time period of 9 p.m. Saturdays - up against NBC's formidable "Golden Girls."

There it has languished, dropping to the bottom third of the Nielsen rankings.

Last month, ABC announced "China Beach" would be placed on hiatus after the Dec. 15 episode and return at an undisclosed date to finish its season run.

Asked if he thought the series would return for another new season, Young replied, "I think it's a possibility, but not a great likelihood."

Young asserts that "China Beach" did quite well in its original time period of 10 p.m. Wednesdays. But when ABC moved it to Mondays and then to Saturdays, viewers couldn't keep up, he said. ABC executives declined comment.

Young countered the network's latest "China Beach" announcement by faxing a copy of his acerbic internal memo to the country's largest news organizations.

Young and Susskind's approaches are high profile, but no one waged a more public campaign to save his show than Barney Rosenzweig, the executive producer of "Cagney & Lacey." Indeed, Rosenzweig may have elevated network pressure to an art form.

The year was 1983 and Rosenzweig was making TV history by producing a cop show starring two women who did not jiggle, have big hair or wear bikinis in the line of duty.

Cagney and Lacey were tough, smart, sometimes grumpy, sometimes self-destructive cops. CBS, citing poor ratings, canceled the show after two seasons.

Rosenzweig, out of a job and his marriage, hit an emotional and professional low. With nothing better to do, he answered all 2,000 fan letters protesting the show's cancellation.

"I said it was my perception that no one in power at the network was reading their mail," Rosenzweig recalled. "I suggested that they write to their local newspapers on the theory that the network executives might not read their mail, but they do read their newspapers."

And write they did. Newspapers followed suit. By summer, the show's ratings began to climb. "Cagney & Lacey," in reruns, captured the No. 1 spot.

In August, the Emmy nominations were announced. Out of five CBS nominations, four were for "Cagney & Lacey."

A month later, the network called to say it had made a mistake. "Cagney & Lacey" was reinstated.

"That had never happened in the history of modern television and it's never happened again," Rosenzweig said.

Now the executive producer of CBS' "The Trials of Rosie O'Neill," featuring former "Cagney & Lacey" co-star Sharon Gless, Rosenzweig said he didn't know if his approach would have the same impact in today's television market.

"I think now it lacks the juice that it had when it was all sort of happening spontaneously," he said.