The fate of Fred Silverman -- for months Topic A in broadcasting circles -- may be decided today, and industry speculation is that he will be fired as president and chief executive officer of NBC. At the same time, "Today Show" host Tom Brokaw is expected to sign a new contract with NBC News after weeks of courtship from other networks, broadcasting insiders said yesterday.

Network spokesmen would be confirm either development but Television Row was giddy with rumors as NBC prepared to welcome the arrival of Thornton Bradshaw, new chairman of parents corporation RCA, who takes over tomorrow. Bradshaw was said to be personally involved in the Brokaw negotiations and rumored to be anxious to present Fred's head at Bradshaw's first meeting with the RCA board tomorrow.

But last week, RCA officially denied rumors of Silverman's imminent departure after first reports of it were circulated by TV Guide magazine in a story not published until yesterday.

Something was definitely in the wind at NBC, however, Spokesmen there confirmed that they had been told to expect a major announcement from RCA today on a "change" in management, and everyone in the public relations department has been put on "stand-by" alert. Brandon Tartikoff. NBC Entertainment president and a Silverman protege, was to leave Los Angeles late yesterday so he could be in New York for today's developments.

Silverman was vacationing in Hawaii, the same place he sweated out the interim between his departure from ABC as programming chief in 1978 and his arrival at NBC in June of the same year. It was expected Silverman, the wonder man of broadcasting, would turn around the faltering company and restore its lost ratings luster. In fact, ratings and profits sank still deeper.

Among the names mentioned by insiders yesterday as possible Silverman replacements were Robert Mulholland, currently president of the NBC television network, and former NBC chairman Julian Goodman. But knowledgeable sources said Bradshaw would go outside the company for the new president and chief executive, and the most conspicuous candidate was Grant M. Tinker, president of MTM Enterprises, estranged husband of Mary Tyler Moore and currently unreachable for comment because he is on a European vacation.

As for Brokaw, an ABC News source confirmed late yesterday that negotiations between him and that network had broken off and that Brokaw was "definitely" staying at NBC.

But NBC sources specified late yesterday that no ink had yet touched paper, and one spokesman said that there were still "fairly substantive issues separating us and him." Lawyers from NBC and Ed Hookstratten, Brokaw's agent, were still "thrashing and bashing" to reach a contract, the source said.

Brokaw himself, reached midafternoon at his "Today Show" office, was coy. "It is not yet resolved," he said, but when asked if it looked as though he would stay at NBC, he replied, "You are leaning the right way." Brokaw leaves tomorrow for England and a short vacation at Wimbledon, so it is widely expected that an agreement will be reached today.

It is still possible, insiders said, that Brokaw will opt for blandishments being bandied about by Roone Arledge, the ABC News president known for his expensive talents hunts. Though CBS News was once also in the running for the boyish correspondent, the field has now reportedly been narrowed to ABC and NBC. Brokaw began his network career in 1966 with NBC.

"Roone wants Tom in the worst way," one NBC insider said. But at the same time Bradshaw has made it a high priority to keep Brokaw on the NBC team, and avoid the impression of the network being deserted by top talent, a network spokesman said.

The game plan, one source said, is for Mudd and Brokaw to become "the Huntley and Brinkley of the '80s," perhaps regaining the news ratings leadership that NBC subsequently lost to CBS and Walter Cronkite (John Chancellor now anchors the "Nightly News," with Mudd reporting from Washington; Chancellor's future in this scheme remains vague). With Dan Rather's ratings at CBS now down slightly from those of his predecessor, NBC may see the chance to move ahead at last.

In order for this to happen, one sources said, Roger Mudd would have to agree to forego a contract stipulation of his own guaranteeing him eventual sole anchorship of the "Nightly News." Mudd, asked about this yesterday, said, "Any announcement to be made will be made out of New York on that." Asked for futher details, he simply repeated that sentence.

At "The Today Show," where Brokaw is known, affectionately if mysteriously, by the nickname "Duncan, The Wonder Horse," a spokesman said that while it was assumed Brokaw would eventually leave the "Today Show" even if he renewed his contract with NBC, the change might not take place until next year. Brokaw has stated he wants out of the early-morning program because he is tired of those 4 a.m. wake-up calls.

The spokesman referred to a memo from Brokaw that has been pinned to the office bulletin board for months, as inquiries continued about Brokaw's future. It says that "a decision has not yet been made and will not be made until later this summer."

Before leaving the office yesterday, Brokaw told the spokesman, "That stands." Later in the day, Brokaw said, "It is a distant possibility that I will remain, but it ain't signed, sealed and delivered, yet."

NBC News president William Small could not be reached for comment.