A Fairfax County Circuit Court jury yesterday found former congressional aide Sewall K. Hoff not guilty of malicious wounding when he struck his neighbor in the head with a meat cleaver last Christmas.

"I'm not guilty," a sobbing Hoff told friends by telephone minutes after the five-man, seven-woman jury returned its verdict. "This whole horrible nightmare is over."

Hoff, 40, a former aide to Northern Virginia Rep. Frank R. Wolf, testified during the two-day trial that he had attacked Richard J. Andrews, 32, in self-defense after Andrews became belligerent and threatened him.

Andrews, who suffered a gaping 5 1/2-inch wound on his forehead in the incident, countered that the attack was unprovoked. He said he was leaving the Hoff house when he turned and faced Hoff and "something struck my skull -- I heard the bone crunching."

It was that unexplained attack that was the weakest link in Andrews' testimony, said prosecutor Stephen H. Moriarty. "I can't say the jury made a mistake," he said. "When you have a lack of an explanation, it's tough for a jury to deal with."

The jury deliberated an hour and four minutes before returning its verdict to Judge Richard J. Jamborsky. Hoff collapsed in his chair and broke into heaving sobs when the verdict was read.

In addition to clearing Hoff of the malicious wounding charge, which carried a penalty of five to 20 years in prison, the jury also acquitted Hoff on a possible lesser charge of unlawful wounding, which carried a jail term of up to five years and/or a $1,000 fine.

The case pitted the credibility of Hoff, a computer operator on Wolf's staff, against that of Andrews, who testified that he had served two years and seven months in prison on drug charges almost 10 years ago. Both men offered divergent accounts of the bloody incident that followed several hours of drinking beer and tequila at Hoff's house late Christmas night.

Despite Hoff's claims of self-defense, Fairfax rescue worker William O. Ray testified yesterday that minutes after the incident occurred, Hoff told him: "I stabbed him Andrews and I hope I killed the son-of-a-bitch."

Prosecutor Moriarty argued that Andrews "walked into a bear trap" Christmas evening when he decided to stop by the Hoff home. He said that Hoff was in a foul mood when Andrews arrived at the house and that relations between the two deteriorated as the night and their drinking wore on.

Hoff testified that he was threatened by Andrews: "He seemed absolutely consumed with a rage to hurt me."

Hoff said he never intended to hurt Andrews, but grabbed a meat cleaver from the kitchen for self-defense. He also testified that he did not swing the knife at Andrews, but rather that Andrews' head struck the cleaver after the man charged at him.

Wolf, a Republican who testified as a character witness for Hoff, said after his court appearance Monday that he had not discussed the possibility of rehiring Hoff. Hoff resigned last December shortly after he was arrested on a charge of malicious wounding.