A prominent GOP activist testified yesterday that he told his former girlfriend he had tampered with her car but made the statement only after she threatened to tell his ex-wife about their affair.

Kevin M. Sabo, a lawyer and member of Virginia's Commonwealth Transportation Board, is accused of cutting the brake lines in the car of his ex-girlfriend, Heather Lawrence, 28. Sabo said he made that and other false statements in phone conversations with Lawrence in March out of fear that the revelation about their affair would damage his relationship with his daughter. He said Lawrence had threatened to reveal their affair if he did not say he was the person who had cut her brake lines, causing her to crash.

"I just went into a panic," Sabo, 38, the GOP chairman for the 11th Congressional District, testified yesterday in Arlington Circuit Court. "It was just terrifying to me that my relationship with my child could be impacted."

The testimony from Sabo, who was general counsel to several committees on Capitol Hill and ran unsuccessfully for the 1992 Republican nomination for Congress in the 11th District, came as his attorney was trying to suppress statements Sabo made to Lawrence during phone conversations she taped at the direction of Arlington County police.

Arlington Circuit Court Judge Joanne F. Alper said she would rule on attorney A. Strode Brent Jr.'s motion at 2 p.m. today. Sabo is to stand trial Monday on a felony charge of attempted malicious wounding of Lawrence in the March 17 crash.

Brent argued that "involuntary admissions" were made by a man who had been treated for depression for several years and, because of his emotional and mental state, was more susceptible to saying things he didn't mean. The attorney also argued that Lawrence had stopped and started the tapes at will and had recorded over conversations. Moreover, he said, she had "lied and threatened" Sabo to cajole an admission out of him.

Deputy Commonwealth's Attorney Theo Stamos argued that it was Sabo who cut the brake lines on Lawrence's car and that he did so because he was upset over the breakup the day before of their affair. The prosecutor said that the couple had a "tempestuous, volatile relationship" and that police had seized numerous tools from Sabo's Annandale home, including one tool that tests showed made the cuts on Lawrence's brakes.

Lawrence, a media relations specialist, was on her way to work that morning in her 1997 Volkswagen Jetta. She drove out of her parking lot in Arlington onto Brookside Drive and "had absolutely no brakes," Stamos told the judge. As her car approached the busy intersection with Washington Boulevard, it crossed a median and crashed into a fence.

Lawrence testified yesterday that she had met Sabo in April 1998 when they both worked for a lobbying firm in the District and that they became involved that summer before Sabo was separated from his wife.

She said she taped "countless" conversations with Sabo to learn if he had cut her brakes and to alleviate her fear that someone was still out there trying to kill her.

"I was scared to death, and I needed some kind of resolve," she said. Lawrence said she taped over conversations because she was running out of tapes and if Sabo confessed, she wanted to capture it on tape. She acknowledged that she made "bogus" threats to Sabo in an attempt to learn the truth, including that she would get word to Gov. James S. Gilmore III that Sabo was a "stalker."

Finally, Lawrence said, Sabo told her that she "didn't have to be afraid anymore." He said he had gotten drunk, had obtained some wire cutters and had done "something to my car," Lawrence said.

Sabo testified that he made the admissions out of "exhaustion," after Lawrence wore him down, attempting to contact him 50 or 60 times. He said she told him that she would not go to police if he admitted the crime.

A police detective, John Coale, testified that after he searched Sabo's home, Sabo told him that Gilmore had appointed him to the transportation board and that the allegation against him "could cause a lot of problems."

"He indicated that he might plead [guilty] to something he didn't do if he could get the matter resolved," Coale testified.