A Fairfax County judge who believes Virginia's drunken driving laws are unconstitutional has begun dismissing cases, including five DWI cases in a week, and has threatened to throw a veteran prosecutor in jail for arguing with him.

Judge Ian M. O'Flaherty made it known in July that he felt Virginia's DWI law unfairly deprived defendants of the presumption of innocence if breath tests showed that they had a blood alcohol content of .08 or higher, levels at which people are presumed to be intoxicated.

"We've been really racking our brains, trying to come up with some solution to it," said Robert F. Horan Jr. (D), the county's longtime chief prosecutor. "It's a crazy situation. He is, for all practical and legal purposes, the Supreme Court of Virginia in these cases, even though, on the Supreme Court, it would take four of him" to issue a majority opinion invalidating a statute.

Critics say O'Flaherty, a General District Court judge, is endangering public safety by returning drunk drivers -- some with alcohol levels of twice the legal limit -- to the roads. But some legal experts are sympathetic, saying the judge might be making a valid argument and protecting the constitutional rights of all motorists.

The judge said in an interview that he recently was made aware of a 1985 U.S. Supreme Court ruling that reversed a Georgia murder conviction because the jury had been told to presume that, if the suspect was "of sound mind," he had the intent to kill.

As it does in all states and the District, Virginia's drunken driving law states that, for anyone with a .08 or higher reading on a breath test, "it shall be presumed that the accused was under the influence of alcohol intoxicants at the time of the alleged offense."

Prosecutors point out that Virginia's law creates a "rebuttable presumption," meaning the defendant has the opportunity to prove it wrong. But O'Flaherty said that wrongly shifts the burden of proof from the prosecution to the defense.

"The Fifth Amendment," said O'Flaherty, 59, "is an absolute protection against requiring the defendant to say or do anything in the course of a trial. . . . The Fifth Amendment means the defendant can sit there, not say or do anything, and at the end of the case say, 'Can I go home now?' "

No other judge in Fairfax -- or elsewhere in Virginia, as far as can be determined -- has joined O'Flaherty. But the judge said some other jurists have told him they agree with him. "I had one judge tell me, 'I'd rule that way, but I don't have the guts to,' " O'Flaherty said. "I told him, 'You should be driving a truck.' "

Prosecutors cannot appeal a case that they have lost at trial at the General District Court level, so they began requesting that charges be dropped before cases went to trial in O'Flaherty's courtroom. O'Flaherty began denying those requests this month.

At least two cases could move toward a state Supreme Court ruling. Both were cases that prosecutors pulled from O'Flaherty's court and then indicted in Circuit Court. One will be tried today in Fairfax Circuit Court.

"This is a public safety issue," said Pat O'Connor, president of the Northern Virginia chapter of Mothers Against Drunk Driving. "My concern is that this judge is putting drunk drivers back on the road, based on a decision that none of his peers have seen fit to agree with."

The judge does have support from some in the legal community.

Ronald J. Bacigal, a criminal law professor at the University of Richmond, said of O'Flaherty: "I think he's exactly right. There are U.S. Supreme Court cases saying you can't relieve the government of proof beyond a reasonable doubt, which is what a presumption does."

Steve Oberman, a Tennessee lawyer and head of the National Association of Criminal Defense Lawyers' DUI committee, said similar arguments about presumptions in the law had been successful in various courts across the country over the years. State supreme courts in Massachusetts and Colorado have ruled exactly as O'Flaherty has on presumptions in drunken driving cases, he noted.

But case law in Virginia has gone the other way, according to Steven D. Benjamin of Richmond, former head of the Virginia Association of Criminal Defense Lawyers. A federal appeals court ruling on Virginia law, based on a driving-while-intoxicated arrest on the George Washington Memorial Parkway, found that a rebuttable presumption "neither restricts the defendant in the presentation of his defense nor deprives him of the presumption of innocence."

O'Flaherty, one of 10 General District Court judges, hears traffic and misdemeanor cases in the morning and felony preliminary hearings in the afternoon. He is one of the most visible judges in Fairfax: He often helps direct people to their courtrooms in the chaotic mornings, and he could be seen raking and blowing leaves from the courthouse's front plaza in autumns past, before a construction project closed the plaza.

The judge is well regarded by lawyers who practice before him and has received high marks in Fairfax Bar Association evaluations. He listens carefully to every last speeder and drunk driver and clearly explains his rulings. He has been a judge in Fairfax for 15 years and said he would like reappointment to another term in 2008. But he also said he would be perfectly satisfied if the legislature decided not to renew him in light of his stance on the drunken driving law.

After O'Flaherty dismissed one drunken driving case in July, in which police said the defendant had a .21 blood alcohol level, and another in early August, Fairfax prosecutors began dismissing the cases themselves before trial and then indicting the drivers in Circuit Court. But Oct. 12, when veteran Assistant Commonwealth's Attorney Kathryn S. Swart tried to do that with a driver who she said had a .20 blood alcohol level, O'Flaherty would not allow it.

Swart argued with the judge, then declined to call any witnesses, prosecutors said. O'Flaherty swore in the defendant and then dismissed the case.

The next day, Assistant Commonwealth's Attorney Jenna Sands asked O'Flaherty to recuse himself from a DWI case, saying it appeared that he would not consider all the evidence. "I'm going to consider all the evidence," the judge told her. "I'm just not going to have a presumption that requires the defendant to testify."

Sands asked him to allow her to dismiss the case so it could be indicted in Circuit Court. "That's denied," O'Flaherty said. "That's unethical. That's called 'forum shopping.' "

Sands tried to argue, but the judge cut her off. "I heard a whining diatribe yesterday from one of your associates," O'Flaherty said. "Next time I hear that from her, I'll put her in jail. You might tell her."

O'Flaherty explained that he had allowed prosecutors six dismissals without cause, so those cases can rise through the system and possibly to the appeals courts, where a formal opinion could be issued. "Half a dozen seems like a reasonable number," the judge said. "After that, there's no reason not to proceed in a regular manner."

He then heard evidence of the defendant's driving and performance on a field sobriety test -- the blood alcohol test was not submitted -- and dismissed the case. Several days later, after receiving evidence that a driver had registered .11 on a breath test but had not failed all the field sobriety tests, he dismissed that case.

O'Flaherty also believes it is unfair to presume that a breath test taken 90 minutes or more after a traffic stop is an accurate reflection of a driver's blood alcohol content at the time the person was driving. Defense lawyers have argued that the blood alcohol content of someone who drinks immediately before driving could still be rising when the person was tested later.

Corinne Magee was the defense lawyer who first won a DWI case in front of O'Flaherty by citing the 1985 Georgia case of Francis v. Franklin. She said the idea to use the Francis case came from everyday discussions among lawyers in the courthouse hallways about how to defend DWI cases.

O'Flaherty said that he was not disregarding blood alcohol results and that he allowed them as evidence when they were properly obtained. But he said alcohol affects people in different ways, so presuming someone with a .08 blood alcohol content is drunk might not be correct.

Similarly, the judge said, "sometimes these tests are taken two hours after" an arrest, and there's no evidence of the blood alcohol content at the time of the traffic stop. O'Flaherty said one way to quickly obtain a blood alcohol reading would be to have a mobile van available with breathalyzer equipment, though he realized that would be costly.

"Criminal law shouldn't be built around saving a buck," O'Flaherty said. "We shouldn't convict people because it's cheaper and easier."