A momentous event that will have no significant immediate effects.

That is how broadcasting industry leaders reacted yesterday to the news that ABC is being sold to Capital Cities Communications Inc. for $3.5 billion, marking the first time a company that includes a television network will change hands, and thus a milestone in the life of American media.

Generally, reaction was positive. "It's great for both sides," said Frank Stanton, former and long-time president of CBS Inc.

"Those are two good and well-run companies, and if you put two good companies together, you are bound to make a better one," said Grant Tinker, chairman and chief executive officer of NBC.

"The better and stronger they become in a very competitive world, the more it enhances all of us," said Gene F. Jankowski, president of the CBS Broadcast Group.

The deal was announced after weeks of speculation that had mostly centered around ambitions to take over CBS Inc., with the predators including Sen. Jesse Helms (R-N.C.) and his so-called Fairness in Media group, and Atlanta businessman Ted Turner. A deposition by Turner made public yesterday confirmed that Helms and Turner had held joint discussions about a possible takeover of CBS.

One could hear in the March wind, however, the ambient noises that accompany ends of eras. The takeover essentially marks the surrender of control of ABC by its chairman Leonard H. Goldenson, whose United Paramount Theaters merged with a then insignificant ABC in 1953 and eventually became the hugely successful and influential American Broadcasting Companies Inc., where were born "Roots," "Dynasty" "Wide World of Sports" and "Happy Days." Goldenson, 79, will remain chairman of the executive committee of the new corporation, but he has relinquished his domain to Cap Cities chairman Thomas S. Murphy.

"It isn't the way I would have wanted to go out," commented Stanton, who is of Goldenson's broadcast pioneer era. "But then, going out for the first generation of any management is just damn tough. The only place I ever saw it work smoothly was at Time Inc." As for the end of an era, "it's worth noting," Stanton said, "but it's nothing cataclysmic of any kind."

"All it indicates," said Jankowski, "is that time marches on."

And NBC's Tinker said that although ABC was the first network to be sold, at least its new owners are within the broadcasting realm. "If somebody totally un-broadcast-related had come in, we'd have some concerns along those lines," Tinker said. "But Murphy is an old pro, as much a member of the club as anybody else is."

The big and obvious question was how ABC would change and how these changes would be apparent to television viewers. One possible effect down the road: the 1988 Summer Olympics from Seoul may be more likely to show up on NBC than on ABC, known as the leading sports network, because Cap Cities' frugality may prohibit the outlay of a huge sum for the rights to the games. ABC already has the rights to air the Winter Olympics that year from Calgary, Canada, and industry sources were quick to point out yesterday that bidding on the summer games has yet to begin.

The ABC Television Network, most visible component of the ABC empire, is just coming out of its worst season in 10 years, and so there would have to be programming changes whether the company was sold or not. Insiders said it would be extremely unlikely Murphy would have a visible impact on the programming to be introduced next fall. The simple mechanics of getting the megadeal approved and of divesting some broadcast properties will take much if not all of his time.

"If you live in Fort Wayne, Indiana, you are not going to perceive any change in ABC," Stanton said. "These changes just don't come about overnight."

"I'd be very surprised to see any noticeable change," said Tinker. Whether Murphy will want to change the people who pick the programs remains to be seen.

"This year has been a bleep for ABC, to say the least," said former ABC Entertainment president Fred Silverman, whose other titles in a colorful career have included NBC chairman. "ABC is at a crossroads. They can recover. All it takes really is three good shows to start the turnaround."

He was asked who was to blame for ABC's current low point. "You can't really point the finger at anyone," Silverman said. "You just have to say 'they.' The damage isn't irreparable at this point, but if they don't have good program development, they could sink further, and then it could take five to 10 years to come around. The biggest single challenge is to get their audience back over the next 12 months. Everything else is all nonsense."

Goldenson's departure from the top spot is no cause for lamentation, Silverman said. "He's had some run there, for Pete's sake."

Tinker said that Murphy's reputation as the Clint Eastwood of cost-cutters could only have promising implications for ABC. "We have, generally, overcomplicated this business and overpopulated our companies," Tinker said. He speculated that a sophisticated network outsider arriving at ABC might notice "an awful lot of bodies in the room" and might perceive that number to be excessive. Tinker's own judicious budgetary pruning at NBC helped double the profits for the network within a year of his own arrival in the chairman's office there.

Asked about possible personnel changes related to the poor network performance, insiders suggested candidates could go as high as Frederick S. Pierce, ABC Inc. president and chief operating officer and veteran ABC career man. "Nobody, Pierce included, can step out from the responsibility for those recent decisions," Tinker said. "Lew Erlicht president of ABC Entertainment doesn't do it in a vacuum. Fred had to be involved in that just as Bill Paley was at CBS, when it comes to final programming decisions.

"While I run around saying it's [NBC Entertainment president] Brandon Tartikoff's ball game, I never disassociate myself from those springtime meetings and the decisions that come out of them," Tinker said.

On the possible replacement of Pierce, Stanton said, "Certainly you have to ask that question."

Silverman said of Pierce, his one-time boss, "I think Fred will come out okay. He's a good executive. He's a very able, bright man. He's just going to have more support from the top than he had before. If I were an odds player, I'd say Freddie is going to come out just fine on the whole thing."

There was speculation that Murphy's cost cutting would mean a radical change in life styles at ABC -- fewer limousines, fewer lavish lunches and fewer generous bonuses and stock bequests to loyal executives. But an ABC spokesman said, "I don't know that we are as 'lavish' as we are made out to be. We don't have a company plane; CBS has four. I don't think we have a 'perky' company. I don't know if we're any more or less lavish than the other guys. While our compensation policies may differ, in terms of what people make here, we are quite similar to our two competitors."

Experts agreed that the deal indicates a volatile new climate for the ownership of TV networks, previously thought to be off-limits to such maneuverings. The deal was made possible in part, sources said, by the Reagan administration's friendly attitude toward big companies getting bigger and changes made in FCC rules under Reagan appointee Mark S. Fowler, the commission chairman, that allow broadcast entities to own more television and radio stations than were previously permitted. Even so, the new corporation will have to unload some of its lucrative stations.

Stanton said, "I think this comes about in some measure because of Jesse Helms and his group. They sent out one million letters urging people to buy CBS stock. That gave a lot of analysts ideas about buying a network. It piqued their curiosity." And though the climate may seem volatile, sources agreed that what ABC gets from the deal is increased stability. "This means it will be a well-managed company," said Silverman. "Murphy is a first-rate executive. That company needs a little order and discipline. It's the right marriage at the right time."

"I don't see any instability at all," Tinker said. "This looks like just what it really is: a well thought-out and well-crafted deal that some very bright people, who were doing business very well, put together." And yet Tinker also said that the exact nature of the deal surprised him: "I thought it would be a merger instead of a takeover."

And the combination of the two companies will make the new ABC much less susceptible to hostile takeovers from outside, sources agreed. For now, anyway.

Tinker said the ABC sale could not be interpreted as a major change in the nature of broadcasting companies since that change has already occurred, gradually over the years.

"These companies passed out of that early Sarnoff-Paley-Goldenson phase without even knowing it," he said, as all three grew large and branched out into other enterprises. "They're not what they used to be even before Murphy shows up. That 'pure broadcaster' phase is yesterday."