In 1976, after graduating from Harvard Law School and serving in the office of the Watergate special prosecutor, Nathaniel Akerman was appointed an assistant U.S. attorney for the Southern District of New York. The next year, Akerman began probing a curious relationship between the mob-controlled Westchester Premier Theater in Tarrytown, N.Y., and the huge conglomerate, Warner Communications Inc.

That investigation has riveted his attention ever since, and now, after six years, the tenacious 35-year-old prosecutor clearly acts like he is on the brink of a major breakthrough in the case.

But his legal tactics--and what opponents call a propensity for shooting from the hip--are getting most of the attention these days.

On Dec. 13, Akerman made an extraordinary accusation in court that Warner Chairman Steven J. Ross is the real culprit in the Westchester Premier affair.

"In our view, the real culprit has not yet been brought to justice," he said. Later, he added: "The real culprit was the chairman of the board of Warner Communications, Inc. and the investigation of him continues."

But Ross never has been charged in the case, which involves several of his top executives and dates back to 1973, when Warner officials allegedly got payoffs in exchange for causing Warner to buy stock in the troubled theater. Westchester Premier was declared bankrupt in 1979 after six theater officials and reputed mobsters were convicted of skimming its receipts.

Akerman made his accusation during the sentencing of two defendants who had pleaded guilty and cooperated with the government in the case, former Warner president Jay Emmett and ex-Westchester Premier executive Leonard Horwitz. Akerman's use of the word "culprit" was defended by Executive Assistant U.S. Attorney Patricia M. Hynes, second-ranking prosecutor in the New York office. "It was important for purposes of that sentencing for the court to have all the relevant facts," Hynes said in response to a reporter's question. "We believe it was important to point out to the sentencing judge . . . where the responsibility should rest."

Ross, 55, an immensely successful executive, called the allegations "outrageous." In making his attack on Ross, Akerman was protected by a prosecutor's immunity in the courtroom.

Criminal attorneys are reluctant to go on the record criticizing a prosecutor because some day they may find themselves trying to negotiate a deal for a client with the same prosecutor. But a number of respected members of the bar say that they were extremely troubled by Akerman's behavior in the courtroom.

One senior attorney here suggested that Akerman's aggressive style reflects his experiences as a Watergate Era prosecutor. A Washington criminal lawyer says Akerman's approach exhibits the "get-the-bad-guys" mentality of the Justice Department strike forces in the 1960s.

At one point during the prolonged litigation, Arthur Liman, Warner's outside counsel and a respected member of the New York Bar, stated in an affidavit that he complained in 1979 to then-U.S. Attorney Robert Fiske about Assistant U.S. Attorney Akerman's "conduct."

Liman complained that Akerman "knew in early April 1978 that my firm had a conflict of interest in representing Warner as well as Messrs. Emmett and Warner Assistant Treasurer Solomon Weiss, yet he refused to disclose the conflict to us. Liman apparently was concerned that the two might be under investigation for misconduct against his other client, Warner.

Describing himself as a former assistant in the U.S. Attorney's Office who is "proud of its traditions," Liman said Akerman's "conduct reflects a different attitude."

Akerman's "culprit" remark wasn't the first time the prosecutor sought to implicate Ross in the scandal. Last month, in his opening statement to the jury in the criminal trial of Weiss, Akerman said: "You will learn how the chairman of the board of Warner Ross designated the defendant Weiss as banker or overseer of a secret cash fund at Warner."

A review of the trial transcript fails to disclose any subsequent reference to a sinister-sounding "secret" cash fund, but a cash fund is mentioned. No testimony showed that Ross designated Weiss "as banker or overseer of a secret cash fund." However, Hynes said "there was evidence in the trial to support that statement."

One criminal attorney blamed judges and Akerman's supervisors for permitting what the attorney regards as questionable conduct. When Akerman made his "culprit" comments during the sentencing of two government witness two weeks ago, presiding Judge Lloyd McMahon said nothing to the prosecutor. However, the transcript in the Weiss trial shows that U.S. District Judge Mary Johnson Lowe did chastise Akerman at the bench after the prosecutor sought to tie Weiss to Ross. "Mr. Ross is not on trial. You have painted that picture," she said. "Let's move on to something else, okay? That just belabors the record and doesn't prove anything."

Another troubling episode in the long and complicated Westchester Premier prosecution occurred in December 1980, during a pretrial hearing in the government's case against Warner executive Emmett.

Under questioning by Emmett's attorney, Edward Bennett Williams, Akerman acknowledged that he knew one of his witnesses, Norman Brodsky, had lied under oath, but had not informed the court.

Williams: "Well, did you believe that testimony by Brodsky to be true at the time?"

Akerman: "It was not true."

Williams: "You believed it to be not true?"

Akerman: "Correct."

Williams: "Did you tell Judge Robert W. Sweet that it was not true?"

Akerman: "No."

Williams: "In fact, didn't you argue to the jury at the end of the case that Mr. Brodsky was an entirely truthful witness and worthy of their belief?"

Akerman: "I forget what the words are, but I did argue that he was credible--his credibility was truthful or he was truthful on the charges and what he said about the defendants, yes."

Asked about this exchange, Hynes provided court papers that she said deal "with that directly." They confirm that, on Feb. 6, 1981, there was a hearing before Judge Sweet growing out of the Akerman-Williams exchange.

However, there was never any resolution of the issue of why Akerman did not tell Judge Sweet that he was aware his witness was giving false testimony. Judge Sweet said in a recent telephone interview that "the issue became moot" when defendants Horwitz and Emmett pleaded guilty three days later, on Feb. 9, and agreed to become cooperative witnesses for the government.