Prince George's State's Attorney Arthur A. Marshall Jr. said yesterday that no charges will be brought against Dona DeFeo, 52, who recently admitted that it was she, and not her son, Angelo, who stabbed her husband to death during a fight in the family home in Riverdale 12 years ago.

Marshall, after a week-long review of police and autopsy records from 1971 and interviews with DeFeo and members of her family, said he could not say for certain whether mother or son stabbed Armando DeFeo, who had worked as a meatcutter.

But Marshall said he concluded that "either or both of them were justified in their action. My personal belief is that Mrs. DeFeo was a woman who was probably just in what she may have done. They will have to live with that."

Angelo DeFeo was charged with murder after his father's death but a grand jury refused to indict him, apparently because it considered the killing an act of self-defense.

Reached yesterday at her home in Oxnard, Calif., where the family moved two years after the killing, DeFeo said she was "relieved" by the prosecutor's decision.

Marshall said he had concluded that the husband's death was "defensible homicide."

"I feel that's true," Defeo said yesterday, "because it was either him or us."

DeFeo told Marshall that on the night of Sept. 14, 1971, her husband came home drunk and started beating her up. When Angelo, then 19, came to his mother's aid, his father began strangling him, the DeFeos later recounted. After years of living with the memory, and in an effort to set the record straight, Mrs. DeFeo confessed to California police earlier this month that it was she who then stabbed her husband several times with a knife.

Mrs. DeFeo's actions, Marshall said this week, were justified in saving her son's life.

For one thing, Marshall said, the father outweighed his son by 36 pounds. And the mother and son "had been threatened that night, threatened constantly," the state's attorney said. " . . . There was apparently a long history of beatings and threats."

Marshall said DeFeo was stabbed with the same eight-inch boning knife that he usually kept under the bedroom mattress, "specifically to threaten family members," Marshall said.

"I never meant to do it, but you never can tell what can happen in an instant," DeFeo said in a recent interview. "I just wanted to make a better life for my kids and protect them. Now that the truth is out, I just want to go on with my life the way I have been."