Lisa Rubin, charged with first-degree murder in the April 24 slaying of her estranged husband, testified yesterday she shot him nine times in self-defense after he pulled a gun and threatened to kill her.

"I had never seen him acting like this before," Rubin told a Montgomery County Circuit Court jury. "I started firing. I just kept firing. He kept coming towards me. I kept firing."

Rubin, the only witness called by the defense, said that after her husband, Timothy Warner, 28, fell on a wooded path in Poolesville, she reloaded her six-shot revolver and fired five times into his back. A .22-caliber Beretta pistol registered to Rubin was found under Warner's body. It had not been fired.

After the shooting, Rubin, 34, said she ran to the nearby Peachtree Veterinary Clinic, where she and her husband of 10 years had arranged to meet to have their dog, Mutley, put to sleep. Rubin, who cried twice on the stand, testified that she then called a private detective and her attorney to report the shooting.

Police were called to the clinic off Route 28 several hours later by Rubin's former attorneys.

On Wednesday, Robert Leopold, one of two private detectives hired by Rubin to investigate her husband, testified Rubin admitted killing Warner after the shooting. "I can't believe it," Leopold said Rubin told him. "I shot him. Is he really dead?"

Rubin testified the shooting began after she told Warner she had implicated him to county police and the FBI in an alleged plot to poison a Secret Service agent who had been her lover.

The alleged attempted poisoning, Rubin said, occurred in January 1989. She testified that Warner confessed to her a year later.

Yesterday, on cross-examination, prosecutor Mark Foley questioned Rubin about an unusual sequence of events that preceded the slaying. Foley noted that Rubin hired private detectives several days after her husband left the couple's Bethesda home in mid-March. A week later, Rubin was observed in a Silver Spring gun shop. She bought two pistols there April 10, Foley said.

According to Foley, Rubin reported the alleged 1989 poisoning attempt to police four days before Warner's death.

Rubin, who refused yesterday to look at photos of her dead husband, said she bought the two guns because she was afraid of her husband. She said she carried the .22-caliber Beretta in her purse and hid the revolver in a bedroom nightstand.

On the day of the shooting, Rubin testified, the .22-caliber gun was missing. Defense attorney Fred Joseph said the weapon Warner allegedly pointed at Rubin was the missing .22-caliber gun. Rubin said Warner had keys to their house after the breakup, but she later testified she had the locks changed shortly before the slaying.