It was a creative legal argument -- perhaps brilliant, some said -- and after a brief reflection, a Fairfax County judge bought it, declaring that key components of the state's drunken driving laws are unconstitutional.

In a decision that could prompt similar challenges nationwide, Judge Ian M. O'Flaherty cited a decades-old U.S. Supreme Court ruling when in the past month he dismissed charges against three alleged drunk drivers.

O'Flaherty, one of 10 judges who preside over traffic cases in Fairfax County District Court, ruled that Virginia's law is unconstitutional because it presumes an individual with a blood alcohol content of 0.08 or higher is intoxicated and denies a defendant's right to the presumption of innocence.

As a district judge, O'Flaherty does not establish formal precedent with his rulings. But reports of the constitutional argument have quickly found their way onto Web logs and into the offices of defense attorneys and prosecutors across the country, prompting some to explore tactics to exploit or attack the Fairfax decisions.

"There will be similar motions everywhere, no doubt about that," said Steven Oberman, chairman of the DUI defense committee at the National Association of Criminal Defense Lawyers. "There are lawyers everywhere who are looking at this issue again in a different light."

A lot will depend on each state's interpretation of its drunken driving laws, Oberman added, and whether a person with a 0.08 blood alcohol level is presumed, by law, to be intoxicated. If so, as is the case in Virginia, other elements must still be proven, including whether the defendant also failed a roadside sobriety test.

Corinne Magee, the attorney whose challenge of the state's drunken driving law led to O'Flaherty's ruling, said the decision was based on the 1985 U.S. Supreme Court case Francis v. Franklin, which dealt with a prosecutor's obligation to prove all elements of a crime beyond a reasonable doubt.

After closely reading the decision, Magee said she realized that it could apply to the state's drunken driving laws.

"I expected him to convict on other evidence in the case," Magee said of O'Flaherty, who presided over the case in which her client was accused of driving with a blood alcohol content of 0.21, more than twice the legal limit.

"I was surprised when he dismissed the case . . . but I think it was based on a very careful reading of the Francis case."

Magee said she was troubled by the law because it presumes intoxication at 0.08 and that the driver was at that level while driving, even if the test was administered hours after the driver was stopped. She said a person's blood alcohol level can fluctuate depending on when the last drink was consumed and how that person's body metabolizes alcohol.

But prosecutors, and even some defense attorneys, disagree, and said yesterday that laws in the 50 states that have established a presumption of intoxication at 0.08 have been upheld even when similar arguments were raised.

"If this ruling became the law of the land, it would be devastating for all DUI cases," Fairfax County Commonwealth's Attorney Robert F. Horan Jr. said. "For all these years, it has passed muster, and now one judge has decided it doesn't. "Our hope is to get it through to circuit court and let it play out and go from there."

Moreover, Horan said, O'Flaherty misinterpreted the obscure and rarely cited 20-year-old case. Because of carefully phrased statutes, defendants in drunken driving cases have to prove they were not intoxicated, he said.

Because prosecutors can appeal only cases dismissed by a circuit court judge, Horan said his office plans to prosecute three other DUI cases in circuit court.

O'Flaherty did not return a call seeking comment.

A. E. Dick Howard, a constitutional law professor at University of Virginia, said O'Flaherty's ruling appears misguided, an "idiosyncratic ruling" that if followed could "create massive upheaval and seismic shock in courtrooms across the country."

"I think the Francis case simply does not apply, not like this," Howard said.

Patrick O'Connor, president of the Northern Virginia chapter of Mothers Against Drunk Driving, said he was not aware of any other state judges who have made similar decisions. O'Flaherty's ruling, he said, undermines the work of law enforcement and prosecutors to keep drunk drivers off the roads.

O'Connor, whose son was killed three years ago in a crash caused by a driver who had a blood alcohol content of 0.15, said he would have been devastated if that driver had not been prosecuted.

"In that case, if they had thrown out that evidence as unconstitutional, then there would have been no consequence for that driver's action," he said.

"I'd be angry . . . at the thought that someone could drink and drive, take a life away and possibly walk free, when all the health and medical evidence support that a driver with .08 is impaired to drive."