A former drug pusher now enrolled in a drug rehabilitation program says on a segment of "NBC Nightly News" scheduled for broadcast this evening that he has made cocaine sales to NBC employes in Burbank, Calif., and used the NBC commissary there as a place of business.

The report is the work of NBC News investigative reporter Brian Ross and producer Ira Silverman, and is being aired tonight partly, insiders say, to quash rumors that NBC was suppressing the report because the network itself is mentioned in it. A source close to Ross and Silverman said yesterday that internal combustion over the report reached the highest levels of network management, including Robert E. Mulholland, president and chief operating officer of NBC Inc.

But Mulholland said later yesterday from his office in New York that this allegation is "totally untrue." He also said, however, that he himself had screened the report earlier in the day--not a common practice for network executives.

"Sure I've seen it. Absolutely," Mulholland said. "Wouldn't you normally look at something in which you are mentioned?" He meant that NBC was mentioned, not him personally. He called the report "an interesting piece of journalism" and said he asked for no changes to be made in it. He said he was unaware that the report had been scheduled for tonight's newscast.

Four attempts were made to contact reporter Ross in the past week regarding this story, but he returned no calls. Producer Silverman declined to comment.

Rumors about the story and what it might contain in the way of revelations have been circulating for some time. The story apparently goes a few steps beyond Frank Swertlow's two-part TV Guide article on cocaine use in Hollywood published in Feburary and March of 1981. An unnamed "high-ranking network official" told Swertlow, "Coke is all over the place. It's directors, writers, producers, actors, everyone. It's horrendous."

According to Paul W. Greenberg, executive producer of "NBC Nightly News," the former pusher interviewed in the report says he also sold cocaine at Universal Studios, which is virtually next door to NBC, and at The Burbank Studios, also within a few minutes' drive. Many network television shows are produced at both studios.

Tom Pettit, executive vice president of NBC News, said yesterday that stories of intense corporate pressure concerning the report were false. "There were no pressures to kill it," Pettit said. "There were pressures to subject it to legal department scrutiny which I fought because once something gets into the legal department, it's hard to get it out."

Pettit said NBC lawyers have been going over the story for about a week and that certain revisions were made, but that "there was absolutely no removal of any material. There was enhancement, for legal purposes, of certain details . . . The simple fact is that it is almost what it was when it went into the lawyers' office."

Reuven Frank, president of NBC News, said last week before leaving for Japan that his only problems with the story at that time were journalistic ones. "We are working on a story. I saw it. I considered it journalistically inadequate and asked for more work to be done on it," Frank said ("Reuven always wants the Second Coming," said Pettit in response). Asked about rumors that the entertainment division of NBC had objected to the report, Frank said, "Nobody from entertainment has been in touch with me."

Reporter Ross has been covering the case of John Z. De Lorean, the former auto industry magnate arrested in Los Angeles in October and charged with intending to pick up and distribute 220 pounds of cocaine valued at $24 million.

There has been speculation within the industry that the Hollywood cocaine story scheduled for tonight's "Nightly News" may have been related to the De Lorean story. Pettit said of the report, "It mentions studios, and it mentions NBC. It doesn't implicate any individual or any company. It will be a big disappointment if you're expecting some sensational disclosures."

Greenberg said Ross and Silverman would continue to pursue the cocaine story and that there may be further reports. "We're not finished with it," Greenberg said. "We're going to keep looking into it until someone comes in and shoots me between the eyes."