Virginia's new, tougher drunken driving laws are likely to put thousands more drivers behind bars each year and require them to install expensive breathalyzer equipment in their cars, lawmakers said.

Drivers charged with having a blood alcohol content of 0.08 or higher will continue to be charged with drunken driving. But those who reach the threshold of 0.15 -- the new level at which tougher laws kick in -- will face at least five days of jail and be required to use a dashboard breathalyzer that prevents them from starting their cars if they are legally drunk.

Offenders pay more than $450 to rent the instrument, called an ignition interlock, for six months.

Before July 1, when 25 drunken driving laws took effect in Virginia, the only first-time offenders who faced mandatory jail time were those with a blood alcohol level of 0.2 or more, and only some repeat offenders were required to put ignition interlocks in their cars.

Virginia has some of the toughest drunken driving laws in the nation.

According to Mothers Against Drunk Driving, about half the states require jail time for all DUI convictions involving high blood alcohol levels. Only four states, including Virginia, require ignition interlocks for such offenders. Neither Maryland nor the District have laws as tough.

Lawmakers estimate that as many as 8,000 additional offenders annually will face those penalties in Virginia, said Del. Robert B. Bell (R-Charlottesville), who sponsored the law lowering the threshold. That would be an increase of more than 300 percent statewide, according to estimates.

Figures from at least one local jurisdiction illustrate the potential increase. In one week in September, for example, 91 people were arrested in Fairfax County for drunken driving, according to county records. Twenty-six of those drivers had a blood alcohol level of 0.15 or more -- nearly three times the number above 0.2.

Proponents say the new laws provide a necessary crackdown on severely impaired drivers, who, statistics show, are involved in nearly 60 percent of alcohol-related traffic deaths.

"These are people that, whether they do it on purpose or not, are doing it at everyone else's risk," Bell said.

The new statutes also have some sheriffs wondering how they will house what could be an onslaught of inmates in already crowded facilities.

At the Fairfax County jail, a staff shortage has meant that an addition completed in 1999 has yet to open, and more than 1,200 inmates are crammed into space meant for fewer than 900, said Capt. Karen McClellan, spokeswoman for the county sheriff's department.

"You're not going to hear us complaining about locking up bad people," said John W. Jones, executive director of the Virginia Sheriffs' Association. "We just need the money to do it."

The new laws also could pose a challenge for the state's 24 Alcohol Safety Action Programs, or ASAPs, that convicted drunk drivers must attend, said Jody Douglas, executive director of the Fairfax County ASAP. Caseworkers at the programs arrange for the installation and removal of ignition interlocks.

Douglas said the process, which entails scouring Department of Motor Vehicles records for offenders' car titles, is so time-consuming that she plans to hire someone just to work on ignition interlock cases. Those could increase by 1,000 a year in the county, she said.

Several patrons at an Alexandria bar said recently that they were unaware of the stricter laws, but most said they know when to stop drinking before getting behind the wheel. Laws and possible social consequences keep them in line, they said.

Navy commander and flight instructor Dave Manero, 38, who is stationed in Pensacola, Fla., said the threat of losing his job over a drunken driving charge is all the deterrent he's needed to remain cautious.

Drinking beer with a friend at Portner's Restaurant in Old Town, Manero said, "It's not just the jail time; it's what a conviction does to the rest of your life. . . . I'm 205 pounds. You ask yourself, 'How much can I drink?' It's an unknown. So you just can't overdo, that's all. You can't be stupid."

Two bankers in crisp white shirts sipped St. Pauli Girl beers and considered that unknown: just how much can someone drink before hitting the 0.15 blood alcohol level.

"About six beers," guessed Don Sweeney, 36. Kirk Purdy, 44, nodded in agreement. "Six beers in two hours," he said.

The general rule is that each drink -- one 12-oz. beer, one glass of wine or 11/4 ounces of liquor -- raises a person's blood alcohol percentage by 0.02, said David Dutcher, executive director of the James River ASAP in Charlottesville.

But that can vary greatly, he warned. Men, who generally weigh more and have faster metabolisms than women, usually can drink more. People who've eaten or who drink slowly will not become intoxicated as quickly. And those who choose drinks like Long Island iced tea -- a potent cocktail made with five liquors -- will probably reach a high blood alcohol level faster than those who sip light beers.

Sweeney and Purdy, both Alexandria residents, said they felt confident they would never reach 0.15 before driving but wondered whether the laws would snare members of the cocktail party crowd along with hard-core, regular drinkers.

"You're punishing people who are no more dangerous than being sleepy," Sweeney said. "It's just a person who has an off night -- literally one too many."

Lawmakers and anti-drunken driving advocates reject that idea, noting that it usually takes knocking back at least a half-dozen drinks quickly to get to that level.

"Social drinking is two glasses of wine, possibly, over dinner," Dutcher said.

Del. David B. Albo (R-Fairfax) said legislators expected to hear complaints about costs associated with the new laws. Albo sponsored a bill, which passed the House but failed in the Senate, that would have required inmates to pay for their jail time.

The General Assembly will reconsider that idea and other sources of funding next year if jails, courts and ASAPs need more money, Albo said. But he and other anti-drunken driving proponents said the new laws will be well worth their cost if they deter people from drinking before driving.

"It's got to be done," Albo said. "There's always a price tag."

Staff writers Lena H. Sun and Leef Smith contributed to this report.

"You just can't overdo, that's all. You can't be stupid," says Dave Manero, right, of Florida, with Mike Spollen of Alexandria at Portner's Restaurant.