Tom Brokaw helped engineer the ouster of NBC News President Lawrence K. Grossman, according to NBC sources at various levels of the company. They say Grossman's resignation this week is a signal that Brokaw's power within NBC has become immense.

"An 800-pound gorilla has been allowed to grow into a one-ton gorilla," one unhappy NBC veteran said. "Tom was clearly a prime mover in getting Larry out of there and was active in the selection process for his own new boss."Grossman himself, reached late Wednesday after what he termed "a nice emotional session" bidding farewell to the troops, said he considered his relationship with Brokaw to have been "straightforward" throughout his four years as NBC News president.

"I heard a lot about that stuff," he said of the rumors regarding Brokaw, "but I have no evidence of anything. Tom and I have had many strong discussions, disagreements, battles, on substance, but all the rest of this stuff I'm in no position to comment on."

In addition to Brokaw, Grossman reportedly fell out of favor with Robert C. Wright, the General Electric executive installed as NBC president when GE took over two years ago. Brokaw and Wright are said to have become friends. The result was a surprisingly public search for a Grossman successor that ended with the announcement of Michael G. Gartner, a lawyer and former newspaper editor, as NBC News president effective Monday, Aug. 1.

"That guy hasn't got a chance either," one skeptical NBC insider scoffed. "If Brokaw doesn't like him, he'll have him fired, too." Brokaw was on vacation and could not be reached for comment.

Grant A. Tinker, the former NBC chairman who recruited Grossman from PBS four years ago, was upset to hear of Grossman's departure and the role Brokaw allegedly played in bringing it about.

"I count Tom Brokaw as one of my friends," Tinker said from Hollywood, where he now runs GTG Entertainment. "But I am disappointed in the people, and I mean any and all people, who participated in getting Larry out of there."

As Dan Rather does at "The CBS Evening News," Brokaw holds the title of managing editor and anchor at "NBC Nightly News." But Brokaw holds another title as well: "chief of correspondents." This gives him a measure of authority, insiders say, over personnel decisions throughout the whole news division.

Grossman said there was "no question Tom has enormous say over who appears on `Nightly News"' but said Brokaw's domain did not extend beyond the boundaries of that program.

In addition to his problems with Brokaw and Wright, Grossman also angered some of those beneath him at NBC News. Initially, Grossman balked at GE orders to perform radical surgery on NBC News as part of budget cutbacks. When Grossman's protest was leaked to the press, Wright became furious with him, and the wound never healed.

Then, when Grossman supervised layoffs mandated by GE, he earned the wrath of NBC News troops. "He alienated people above him, and he alienated people below him," one associate said. Eventually some 300 jobs were eliminated.

The ouster of Grossman, says one NBC expatriate, is part of GE's effort to reshape NBC along more traditional corporate lines, to make it resemble the GE divisions that make toasters and turbines: "They inherited the most successful company in the history of broadcasting and they're turning it into whatever it is they want it to be."

Another NBC insider said, "The only question around here is, when will GE sell the place? To them, we're just a commodity."

No GE spokesman would comment on that or any other aspect of the story.

Although he had many successes within the division, Grossman reportedly told a colleague early this year that if ratings didn't rise for "NBC Nightly News," he knew he was "a goner."

The opinion that counted most in this case, however, was apparently Tom Brokaw's. The departure of Grossman is another sign of changing times in network broadcasting, and even those who are among Grossman's detractors do not seem to find such signs encouraging.