Fred Silverman once credited Perry Laffety, a former boss during Silverman's days at CBS and later on the Silverman team at NBC, with the cautionary advice, "It's not a crusade, Fred," in reference to the ratings rat race of network television.

Silverman probably forgot that advice many times during his frenetic three years as president and chief executive officer of NBC; it did become a crusade, and yesterday, the crusade was over and the crusader turned in his scabbard. NBC, in third place when Silverman took over in June of 1978 -- at a salary of a $1 million a year -- was still in third place, and pretax profits for the television network had declined from a reported $125 million in 1977 to $10 million for 1980.

The man whose arrival at NBC had been greeted in 1978 with a hoopla and huzzah not sen since de Gaulle marched into liberated Paris was forced into retreat and a virtual admission of defeat. Some will say Silverman his control -- such colossal bad luck as the collapse of NBC's plans to televise the 1980 Moscow Olympics after the United States withdrew from participation -- and some will say he was a victim of his own limitations, a man who prospered in television under the old rules but who couldn't play by new ones that he himself had helped bring about.

He may in time be remembered as televison's last tycoon. New, competing forms of television like pay cable are steadily eroding the total network share of the U.S. viewing audience, and networks may never again exert the enormous, pervasive influence they once had over America's heart and mind. Silverman was still trying to pull rabbits out of hats and do other magic tricks in an age that has surrendered to the computer and the market researchers.

In a forthcoming book on Silverman, "Down The Tube: Prime Time TV in the Silverman Ears," TV Guide reporter Sally Bedell, who last week was first to break the news to Silverman's departure, analyzes the executive acclaimed, "the man with the golden gut" for this programming instincts as "neither wizard nor genius" but "a manchild in the once-promising television wasteland" who knew "all the manipulative rules of the game" but played it "for the sheer joy of it."

She profiles Frederick Silverman, son of a TV repairman, as a TV baby who never completely lost his starry-eyed enthusiasms and zest for success -- a drive more comparable to a high school student's yearnings for gold stars and straight A's than a lust for riches and luxury, two things that have never appeared to matter much to Silverman anyway.

At NBC, Silverman always had an uphill fight -- against an entrenched, stodgy, long self-satisfied establishment he used to refer to as a "romanian bureaucracy," for one thing. But Silverman was also trying, especially in his first two years at the network, to dispel the image of TV's eminent vulgarian he earned in three wildly successful years as president of Abc Entertainment starting in 1975.

In that period Silverman fostered or helped create such profitable buy critically derided programs as "Charlie's Angels," "Laverne & Shirley," "The Love Boat" and "Fantasy Island." But Silverman also went to bat for the television landmark "Roots," and himself came up with the plan to telecast it for eight consecutive nights, instead of in weekly installments. "Roots" became the most-watched and also one of the most honored television programs in history.

At CBS, where he was a programming vice president for five years prior to his arrival at ABC, Silverman was among those executives who championed, over the strenuous objections of CBS' chairman and founder, William S. Paley, "All in the Family," the trailblazing 1971 Norman Lear production that revolutionized situation comedy in television.

Where Silvermen differed from other TV executives was in his passion and limitless appetite for television and for competitive programming. Visitors to his office might find themselves disarmed by the sight of Silverman plopping a cassette of a new sitcom onto his machine and slapping his desk with appreciative laughter. In Bedell's book, Lafferty recalls finding Silverman in tears over an episode of a soap opera. "all that stuff is totally real to him," Lafferty said.

And so Fred Silverman may always hold the title of Ultimate Television Executive -- perhaps Ultimate Television Being -- even though a combination of misfortune and his own alleged shortcomings as an administrator and delegator of authority kept him from grabbing his third brass ring, after smash success at the other two networks.

In recent weeks, industry observers noticed a change in his usually irrepressible personality. He was growing moody. He was giving "I'm tired" interviews. The man who always thrived on competition and the hurly-burly of what Bedell calls "the most visually competitive business in America" seemed finally to be wearying of the crusade.

But until that time, he never ran out of brave predictions for the future, and those who know him have said his proclivity for finding silver linings and wrapping himself in them was born of total sincerity.

In 1979, after just over a year in his new Rockefeller Center office, Silverman said, "I ultimately have got to take the responsibility for the success or failure of this company. I've made it very, very easy: I said by December of 1980, we'd be first, and I'm willing to stand by that. I don't have anything up my sleeve except a lot of hard work and careful planning."

Silverman's manner with employes alienated some, endeared others. He was known for making animated telephone calls in the middle of the night to those on his staff, often to describe some bold new project that had popped into his brain. His temper tantrums were as legendary as his nearly interminable conferences.

But Silverman's problem at NBC may stem from what some see at his Achilles' heel: an uncanny ability to schedule existing strong programs for their maximum audience-luring effect, but an inability to instiguate new programs with that potential. At NBC, he inherited a miserable schedule and was never able to improve it substantially, despite such fitful smash hits a last fall's mini-series "Shogun."

He was still the master builder. He just didn't have any blocks to build with. After arriving on the scene as the newly reformed Respectable Fred, Silverman was soon forced by competitive forces to resort to the old titillations to woo viewers -- bosomy women in revealing attire, as on such irredeemably leaden romps as "Sheriff Lobo." In October 1979, Silverman defended such practices as good business for starting a TV season.

"Going in, you will use every trick in the book," Silverman said. "That's showmanship." But he also pledged to stick by such projects as the lofty-minded "Live from Studio 8-H," hoping to counter the Bad Freddie image with prestigious, loss-leader Good Deeds. "For every 'Lobo,' you really must move in a totally different direction, and I think we will. I know we will," he said.

A few of those who left NBC during Silverman's reign despise him and refer to him as emotionally irresponsible. But at least Silverman retained a bravado that made him a magnetic and charismatic, if often inscrutable, public figure -- a lone maverick among the new plain breed of TV executives, a successor, at least in terms of moxie and gusto, to such fabled movie maguals as Hary Cohn and Louis B. Mayer. If he is the last of a breed, that's the breed it is.

Asked once why he recived so much more media attention than comparable executives at other networks, Silverman said, "I guess there are very few people to write about right now. In past years, we had very colorful people in televison. Ten years ago you had people like Frank Stanton, Mike Dann, Mort Werner, Bob Kintner, Ollie Treyz, Jim Aubrey -- it was a very colorful group of people. Now, for the most part, there aren't too many individuals. The overall impression now of executives in television is that they're a much grayer group that they've been in the past."

In his surprisingly modest office on the sixth floor of NBC's Rockefeller Center headquarters, Silverman kept a few mementoes of his spectacular comet-ride at ABC. One was a signed picture of Laverne and Shirley (Penny Marshall and Cindy Williams) that said, "To Fred, who made us what we are today -- tired!"

Another was a Lucite paperweight forged to commemorate the fact that ABC had, under Silverman's guidance, overcome the 20-year dominance of CBS to become the No. 1-rated network (a status surrendered back to CBS after Silverman left). "We'll have a new one of those made for Christmas 1980," Silverman said in September 1979. "Listen, by Christmas 1980, if it doesn't happen, I'll be coming to you for a job. I'll say, 'Do you need somebody to get coffee around here? A go-fer?

Silverman also said then that under his regime, laughter had returned to the halls of NBC, though it would later pretty much die out. "That's the only way to get through a day," he said then. "Gotta have a couple of good laughs every day and say, "The hell with it.'" Fred Silverman said the most dazzling career in American broadcasting, and the transitional decades of the '70s, behind him.