Robert R. Barrow, charged with first-degree murder in the June 11 death of his wife, broke into tears on the witness stand yesterday as he described an angry fight that ended when he shot Nancy Barrow three times and stabbed her with a kitchen knife.

In a low voice that cracked with sobs, Barrow, 46, told an Arlington Circuit Court jury he had no intention of killing his wife and had brought a gun to her North Arlington house that night because he had contemplated killing himself. Barrow has pleaded not guilty.

Police, responding to calls of a domestic disturbance, said they found Nancy Barrow, 44, dead on the kitchen floor of three gunshot wounds and a stab wound. The killing occurred shortly before the couple's divorce was scheduled to become final. The couple had separated in January 1984 and a joint custody arrangement for their 9-year-old son, Jason, was awaiting final court approval.

On June 11, after arguing over an agreement to sell the house at 4818 N. 25th St. and over the division of their 1984 tax returns, Barrow testified: " Nancy said she was going to take Jason away from me. And not only that, she said she could do it because I wasn't his real father."

Barrow's attorneys, Mark B. Sandground and John W. Karr, have maintained that Barrow killed his wife "in a moment of absolute blind passion."

Barrow said he "was shoving the tax papers back in the bag . . . and I came across the gun," a five-shot, .38 caliber antique revolver.

"Then?" asked Karr.

"The gun went off," Barrow said.

"Whose hand was it in?"

"I don't know; mine, I suppose."

Barrow said his wife then got a knife from the kitchen. "We were struggling with the knife, and we fell, and I guess I stabbed her."

"You guess?" Karr asked.

"I stabbed her, I stabbed her, I stabbed her," Barrow said quietly.

In 3 1/2 hours on the witness stand, Barrow broke into tears several times, pounding the stand with his fist and sobbing.

Under cross-examination by Assistant Commonwealth's Attorney Frank Soulier, Barrow said he could recall few details of the incident.

"Explain to the jury how you ended up stabbing Nancy," Soulier said.

"I can't. I just stabbed her," Barrow answered.

"So your testimony to the jury is that you don't quite remember this incident at all. Is that right?"

In a low, even voice, Barrow said, "I know I shot her. I know I stabbed her. I know she's dead. And I know Jason's an orphan."

Barrow testified that, beginning in 1974, he learned of a love affair his wife was having, the first of a succession of affairs that he said she would flaunt by leaving letters from her lovers around the house.

Colleagues, friends and relatives of Barrow testified yesterday that his work, his personal habits and his mental attitude deteriorated during the last years of his marriage.

Barrow said he had brought the gun from his grandmother's Pennsylvania home in 1984. "I was considering ending my life because I didn't want to lose Jason," he said.

The eight-man, four-woman jury is expected to begin deliberations today.