Ten days after he was released from jail in exchange for pleading guilty to charges of beating his wife, who refused to testify against him, a Queens man decapitated the woman and their 7-year-old son late Sunday night and stabbed his 13-year-old stepson to death, the authorities said.

The man, Richard Lyle Timmons, 33, then slashed one of his wrists in an apparent suicide attempt, the police said. He was taken to Bellevue Hospital Center for surgery and was later released. Late last night, he was charged in the killings of his wife, Annita Stewart Timmons, 33, their son, Aaron, 7, and her son, Sharron, 13.

This is the latest of several recent New York cases in which a husband accused of beating his wife has violated a court order of protection and murdered her.

Mr. Timmons was freed from jail after he agreed to plead guilty to beating his wife. In exchange for his plea, a judge sentenced him to a year in prison, which paved the way for release because Mr. Timmons had already served nine months in jail awaiting trial.

Mr. Timmons went on trial May 13 in State Supreme Court in Queens on charges that he broke his wife's eye socket and then held her at knifepoint for two days, refusing to let her get medical attention, and that on another occasion he threw her through a first-floor window. His wife refused to testify against him at the trial, but prosecutors had planned to use her past statements to the police, other witnesses, medical records and photographs to make their case.

''Because the victim in this case refused to testify, the judge felt that the likelihood of a conviction was slim,'' David Bookstaver, a spokesman for the Office of Court Administration, said.

Mr. Timmons was freed by Acting Justice Robert J. McDonald on May 29 after he entered a plea agreement, over the objection of prosecutors, in State Supreme Court in Queens. Mr. Timmons pleaded guilty to nine counts of assault, unlawful imprisonment, menacing and criminal possession of a knife, charges that carry a maximum sentence of seven to nine years in prison.

Mrs. Timmons was given a limited order of protection, allowing her husband to see her and the children but not to threaten, harass or intimidate them. ''We opposed the plea. We opposed his release. We opposed the limited order of protection,'' said Mary de Bourbon, a spokeswoman for the Queens District Attorney, Richard A. Brown.

Neighbors said that Mr. Timmons moved back last week to his wife's apartment on the sixth floor of 35-12 35th Avenue, one of the Ravenswood Houses in Long Island City, Queens.

''I'm surprised she let him back in the house,'' said Raymond Johnson, 29, a neighbor on the same floor who recalled the past abuse. ''I would see her with her eyes black.''

Shortly after 11 P.M. on Sunday, the police said, someone dialed 911 from the apartment but did not speak. When the police arrived, they broke down the door and found Mrs. Timmons and Aaron with their heads cut off and Sharron stabbed to death. Inspector Robert K. Cividanes of Queens Detectives, who has been visiting grisly crime scenes for 34 years as a police officer, said it was the worst he had ever seen. The police removed a hatchet and a knife from the apartment, he said.

In the recent trial, Mr. Timmons, who was jailed in 1982 for robbery and in 1986 for petty larceny, stood accused of abusing his wife in three incidents, on June 29, Aug. 9 and Sept. 7. At the trial, officials said, Mrs. Timmons refused to testify. At a special hearing, she denied that her husband had threatened her to keep her from testifying, Ms. de Bourbon said.

Karla Digirolamo, who runs Families in Crisis, a domestic violence program in Troy, N.Y., was then asked to testify for the prosecution about the reluctance of some women to testify against their abusers.

''There are three main reasons,'' she said in an interview. ''Fear, love -- and all the confusion that comes when fear and love come from the same place -- and the practical barriers of housing, money and that kind of thing.''