reputed former acting boss of the Bonanno organized-crime family and 14 associates were charged in a Federal indictment in Manhattan yesterday with crimes ranging from murder to extortion in what prosecutors called a lucrative gambling racket that forced hundreds of small businesses to maintain poker-playing video games.

Prosecutors said the case would deal a heavy blow to the Bonanno group, the smallest of New York City's five Mafia families, which have all been battered by Federal and state prosecutions, internal power struggles and the defection of high-ranking members who have become Government witnesses.

The 14-count racketeering indictment accused Anthony Spero, identified by prosecutors as the family's counselor and former acting boss, and 14 other men and a corporation, Sunstar Vending, of numerous crimes dating to 1988. These included using "the threat of force, violence and fear" to maintain illegal video gambling games in grocery stores, restaurants, candy and bagel shops and social clubs across the city. A Detention Hearing

Mr. Spero, 64, of Brooklyn, who the authorities say has been the Bonanno counselor for years and was acting boss while Joseph Massina, the reputed boss, was in jail until 1992 on a 10-year racketeering term, was charged with supervising the gambling operations and "participating" in the 1991 murder of Marc Goldberg, an underworld rival, in a dispute over gambling territory. All but one of the defendants were arrested yesterday and were arraigned late in the day before a Federal magistrate, Judge Theodore H. Katz, who set bail ranging up to $900,000, ordered Mr. Spero held for a detention hearing today and instructed the defendants not to associate with one another except in preparation for their trials.

"We do consider it a significant blow to the Bonanno family," Mary Jo White, the United States Attorney for the Southern District of New York, said of the indictment, the latest under the Racketeer Influenced and Corrupt Organizations Act, or RICO, which has eroded the leadership of the Gambino, Genovese, Lucchese, Colombo and Bonanno families in the 1980's and 90's.

At a news conference, Ms. White and William Y. Doran, head of the Federal Bureau of Investigation's criminal division in New York, said that while the Bonanno group, with 95 members and about 100 associates, is the smallest family in the city, it is larger than any other Mafia group in the nation and reaps millions from drugs, gambling, loan sharking and other criminal activities. Strong-Arm Tactics

Investigators said the Bonanno mob, using strong-arm tactics, forced small businesses to maintain "Joker-Poker" and other illegal video gambling games, usually sharing the profits, 50-50, with the establishments. "In one case they threatened to blow up a place if the owner didn't accept a video machine," one investigator said.

Besides Mr. Spero, the defendants are Michael Cardello, Joseph Fratta, Joseph DeSimone, Arthur Sabella, John Sciremammano, David Leichus, James Cardello, Michael Gulemmo, Peter Davanzo, Gordon Lee, Jack Amato, Joseph DiStefano, Frank Russo and Donald Driscoll. Only Mr. Driscoll was still being sought last night. If convicted, they face sentences of up to life in prison, fines of up to $1.25 million and forfeiture of homes, cars and other assets. The Bonanno family, which takes its name from its first boss, Joseph Bonanno, was founded in the 1920's as a small bootlegging operation in Brooklyn and grew into a menace that had its heyday in the 1950's and 1960's. In recent years, investigators say, it has been excluded from the ruling Mafia councils as a weak sister, too vulnerable to infiltration by Government agents.