Drunken driving convictions are about to get harsher in Sacramento County.

Motorists found guilty of a first drunken driving offense here and in three other California counties will be required to install and use breathalyzers in their cars for five months, under a law signed this week by Gov. Arnold Schwarzenegger.

The ignition interlock device will keep the car from starting if the driver’s breath shows more than a small amount of alcohol in the blood.

The law will be tested in a six-year pilot project here and in Alameda, Los Angeles and Tulare counties. It goes into effect July 1, 2010.

“We must do everything we can to ensure the public’s safety on the road,” Schwarzenegger said after signing the bill. “By installing ignition interlock devices we are making it harder for DUI offenders to get behind the wheel while intoxicated and we are working to save innocent lives.”

The American Beverage Institute, a restaurant trade association, had urged Schwarzenegger not to sign the bill, calling the locks intrusive and saying the state should target repeat offenders.

The law initially could affect 4,000 first-time drunken drivers per year in Sacramento County, based on state reports.

In Sacramento in 2006, more than 5 percent of those offenders were involved in a DUI crash or arrest within a year, state data show.

Assemblyman Mike Feuer, D-Los Angeles, says he believes the program will reduce first-time offender numbers and recidivism rates.

Feuer said he hopes the law will show enough progress in Sacramento and the other counties to persuade lawmakers to implement it statewide.

“We have a problem of enormous consequences in the state,” Feuer said. “I’m pleased we could get a toehold in California.”

Officials with Mothers Against Drunk Driving called the law a significant step in using technology to reduce roadway deaths.

Seventeen states already have similar laws, and some have shown notable drops in repeat drunken driving offenses.

Ignition interlock devices are not new in California.

The state already allows judges, at their discretion, to require drunken drivers to use such systems, but anti-drunken driving advocates say judges often don’t take advantage of that provision.

Under the law, drivers convicted of a first offense will be notified by the state Department of Motor Vehicles that they must pay to have a device installed in any vehicle they drive, other than a motorcycle.

If a first-timer’s conviction involves an injury crash, the device must stay in the vehicle for a year.

For second-time DUI offenders, the monitoring period will extend to a year. A third conviction will require the device be installed for two years.

Initial installation costs $75 to $100, Feuer said, and monthly monitoring costs run $50 or more.

It is illegal for another person to blow into the device for the offender, said Mary Klotzbach, California MADD policy director.

The devices also require drivers to retake the breath test at random times, she said.

If the driver fails the test or doesn’t pull over to take the test, the car will not immediately stop, but the failure will be recorded by the device and forwarded to county officials.

Drivers whose incomes are low will be required to pay only a portion of the cost. The device manufacturer must absorb the rest of the cost, Feuer said.

Feuer said he has lined up federal grants to pay for DMV’s costs of administering the program.

DMV will be required to provide an analysis of the program’s effectiveness to the Legislature by 2015.

California and other states have been on a push in recent years to reduce drunken driving injuries and deaths. Numbers have dropped, along with other types of crashes, but they remain substantial.

In 2008, 30 percent of roadway deaths in California � more than 1,000 deaths � occurred in crashes where at least one driver had a blood- alcohol level over the legal presumptive limit of 0.08 percent, according to the state Office of Traffic Safety.

Feuer said Sacramento County was chosen as one of the test sites because officials here supported the measure and because Sacramento County has a notable drunken driving problem.

The city of Sacramento, in particular, has the highest drunken driving injury and fatality rate among the state’s largest cities, an analysis by the state safety office showed.