Alcohol-related deaths on Fairfax County roads decreased by 44 percent last year despite more vehicle miles traveled in the county, apparently running counter to a statewide trend.

Fifteen persons died in 13 alcohol-related traffic accidents in 1987, down from 27 deaths the year before, according to a report released last week by the Oversight Committee on Drinking and Driving, a group appointed by the Board of Supervisors to monitor drunken driving trends in the county. The decrease was "the most dramatic drop in alcohol-related fatal traffic accidents in more than a decade," the fourth annual report said.

Alcohol was a factor in about a third of the 45 traffic deaths in Fairfax County last year, according to the report. Seventy-five persons died on county roads in 1986.

The report said it was unclear why the number of alcohol-related traffic deaths had dropped, but it cited increased police enforcement, public information campaigns, greater use of seat belts, school initiatives, rehabilitation services and private sector programs as possible factors.

Statewide, preliminary statistics show "a possible 10 percent reduction in all fatal accidents but at least a 4 percent increase in alcohol-related crashes" last year, according to the report. It says early data from the National Highway Traffic Safety Administration shows a slight increase in traffic deaths nationwide and a decline of 1 percent or less in alcohol-related crashes.

The decrease in deaths in 1987 came despite an 8 percent increase in vehicle miles traveled on county roads and a 4 percent increase in the number of licensed drivers and vehicles registered in the county, according to the report.

It says initial figures show that, statewide, alcohol sales were down an undetermined amount, while the sale of beer was up 8 percent over the year before and wine sales possibly dropped a little.

The county Police Department investigated 19,500 traffic accidents in 1987, down 1 percent from 1986, and alcohol was a factor in 8 percent of them, according to the report.

Police charged 3,626 people with driving while intoxicated, up from 3,563 the year before, and convictions were obtained in about 87 percent of the 5,619 DWI cases tried in Fairfax County General District Court. Of the 4,838 people found guilty, 687 had previous drunken driving offenses.

Sixty-seven persons under age 18 were arrested for driving while intoxicated in 1987, about the same as the year before.

"The number of habitual offenders who escape prosecution and rehabilitation continues to be a growing problem," the report states. "In 1987, 482 Fairfax County residents were certified by the Virginia Department of Motor Vehicles for processing as habitual offenders by the Fairfax County commonwealth's attorney. Only 135 (28 percent) were processed as required by law."

About $847,000 in fines for drunken driving was collected, with the average fine being $225, and 1,313 people had restrictions placed on their licenses.