Federal prosecutor Nick Ackerman today accused Steven J. Ross, the chairman of Warner Communications Inc., of being the "real culprit" in a criminal probe of his company's dealings with now-defunct Westchester Premier Theater in Tarrytown, N.Y.

Ackerman, who made his startling accusation at U.S. District Court here during remarks prior to the sentencing of two other executives involved in the case, said the investigation of Ross was continuing.

Ross, through a spokesman, denied any wrongdoing and called Ackerman's statement "outrageous."

The government, in its complex six-year investigation, has contended that top Warner executives got kickbacks from the Westchester Premier Theater in 1973 in exchange for using the corporation's funds to buy stock in the financially troubled theater.

At today's hearing, Judge Lloyd F. MacMahon sentenced Jay Emmett, 55, a former president of Warner, to a 10-year suspended sentence and a fine of $20,000. Emmett pleaded guilty in February, 1981, to two felony charges of transporting in interstate commerce two Warner checks "knowing these checks to have been stolen . . . and taken by fraud."

The other executive, Leonard Horwitz, 58, who once was a vice president of the Westchester theater and briefly a Warner publicity executive, was also given a suspended sentence and placed on probation for three years for tax evasion in the case. Earlier, he served nine months of a three-year sentence for stock fraud and obstruction of justice stemming from the Westchester theater investigation.

Both men were government witnesses in the trial last month of Solomon Weiss, assistant treasurer of Warner. Weiss was convicted on Nov. 27 of racketeering and bribery charges for his involvement in the Westchester theater stock deal.

Today, Ackerman told the judge that the two men had cooperated with the government "thoroughly" and "truthfully." As a condition of their "special probation," Horwitz and Emmett were directed by Judge MacMahon to "continue to cooperate with the government."

Ackerman, in his remarks on Horwitz's sentencing, said, "The real culprit has not yet been called to justice."

Later, in the presentencing remarks on Emmett, Ackerman said: "The real culprit is the chairman of the board of Warner Communications Inc., and the investigation of him is continuing."

Last night, Ross, through Warner general counsel Martin D. Payson, was quoted as saying: "I have done no wrong and these accusations are outrageous."

This is not the first public reference by Ackerman to Ross, who has directed the growth of Warner into a $3.2 billion conglomerate. During his opening statment to the jury in the Weiss trial, Ackerman said: "You will learn how the chairman of the board of Warner designated the defendant, Weiss, as banker or overseer of a secret cash fund at Warner."

However, this was the last mention of any "secret" cash fund in the trial. And government witness Emmett admitted under cross examination that he was "the only person in the entire world to attribute a direction of this cash fund to Ross."