For the second time in a week, D.C. Council members asked Police Chief Charles H. Ramsey to explain the arrests of drivers with blood alcohol levels below the legal limit for intoxication.

On Monday, Ramsey acknowledged being confused about why the council plans to change the city's drunken driving law. Yesterday, Ramsey issued a full-throated defense of existing laws and his officers' actions in a few high-profile cases.

"We're at a point where traffic fatalities are the lowest in 20 years,'' Ramsey said. "I don't want us to slip.''

Ramsey said the public misunderstands the department's criteria for charging people with driving under the influence, or DUI. District law, like laws in Virginia and Maryland, allow for the arrest of any driver a police officer judges to be impaired, regardless of blood alcohol level.

Attorney General Robert J. Spagnoletti, who joined Ramsey in testifying before the council's Judiciary Committee, said: "There is no evidence to suggest that this is a big problem in the District of Columbia. The system works. The number of deaths declining suggest we're doing it right."

Last week the council passed emergency legislation that would bring D.C. law closer to laws in surrounding states. But Spagnoletti said the changes affect only the presumptions that are used in court. They do not change the threshold for arrest: an officer's probable cause to suspect that a driver is impaired by alcohol or drugs.

Spagnoletti said many DUI arrests in which drivers have a blood alcohol level below .08, the legal level for intoxication in the District, also involve drug use, which cannot be measured with a breath test.

In 2004, D.C. police made 521 arrests for driving while intoxicated, or DWI, and 165 for DUI. Police also arrested 103 people who refused to be tested. Those totals do not include arrests made by the U.S. Capitol Police and others.

The Washington Post has published stories about the arrests of drivers with low blood alcohol levels. One report was about the experience of Debra Bolton, a 45-year-old Virginia woman, who said she was arrested for DUI and spent five months fighting the charge after drinking one glass of wine with dinner. Her blood alcohol level was .03, and her case was not prosecuted.

Spagnoletti and Ramsey took issue with her story, saying she did not pass any of the four field sobriety tests administered by the arresting officer. In an interview, Bolton said that after the officer told her she was under arrest, she replied: "Why? I passed all your little tests."

Ramsey defended the action of the arresting officer, Dennis Fair, who made 14 DUI arrests in 2004, the second-highest number in the department, according to Ramsey's written responses to the committee's questions. Fair is one of the 90 D.C. officers specially trained in detecting impaired drivers.

"If you have a person who can't pass a field sobriety test, who is driving without lights, these are signs of impairment,'' Ramsey said of Bolton's arrest. "Everybody's up in arms about it, but I think the officer did the right thing.''

In an interview yesterday, Bolton stood by her story.

"I was not impaired in any way," she said. "I didn't fail any of the tests. There are discrepancies, in my opinion, between what happened that night and what the police report showed. But I don't have a chance to have my say. It's entirely the discretion of the police officer. The problem is, it's his word against mine."

For example, Bolton said, Fair told her that he was arresting her because he smelled alcohol on her breath. The police report made no mention of that.

Council member Phil Mendelson (D-At Large) asked why people are arrested with low blood alcohol levels when it is unlikely that they will be prosecuted.

Staff writer Brigid Schulte contributed to this report.

Police Chief Charles H. Ramsey, shown in June, has said he doesn't want DUI enforcement to slip.