Virginia man with "a heart bent on mischief," in a prosecutor's words, went on trial here today, apparently the first driver in the state charged with second-degree murder in an alleged drunk driving case.

The defendant, Warren Wesley Essex, 25, who Fauquier County prosecutors contend "knew or should have known" his acts might result in injury or death, faces three second-degree murder counts and a drunk driving charge in a trial being watched closely by advocates of stiffer penalties for alleged alcohol abusers in Virginia.

Essex was indicted in January in connection with a head-on crash last November on a country road about 50 miles west of Washington. Two teen-age girls returning with a brother of one of them from a Culpeper bowling alley were killed. The brother was not seriously injured. A passenger riding with Essex also was killed.

If convicted, Essex faces a maximum penalty of five to 20 years in prison on each murder count. Conviction on a manslaughter charge -- an option that the jury may choose -- is punishable in Virginia by one to five years imprisonment and a $1,000 fine.

The parents of two victims, Nora Lynn Neale, 17, and Deborah Lynn Gouldthorpe, 16, were among the spectators in the modern, sunken courtroom. Donna Neale, mother of one of the girls and president of a local chapter of Mothers Against Drunk Driving, a group that has lobbied the Virginia legislature for stronger laws governing drivers who drink, clutched an 8-by-10-inch color photograph of her deceased daughter to her breast throughout the day.

Essex, an employe of a Warrenton contracting firm who is free on bond, sat impassively in the courtroom, dressed neatly in white shirt and tie and a sleeveless pullover sweater. During brief recesses he walked the courthouse corridors, sometimes holding his 4-day-old son.

Assistant Fauquier prosecutor Roger Inger said outside the courtroom yesterday that he and Commonwealth's Attorney Charles Foley decided to bring the murder charges after their research showed that prosecutors in 11 states across the country have succeeded in winning similar convictions.

"It's a matter not of what he did but how he did it," Inger said. He said the prosecutors believe murder charges may be easier to prove than involuntary manslaughter, the charge commonly brought against alleged drunk drivers, but which requires the state to "show and prove" acts of gross, wanton negligence.

"Murder requires that we show callous disregard for human life, that he knew or should have known that grievous injury or death might follow from what he did -- in other words, the definition of malice," Inger said.

Since the Essex indictment, Foley and Inger have brought similar murder charges in a case involving a Fairfax County woman who, prosecutors contend, was drunk when she allegedly caused the deaths of two women in a May 1 crash in Fauquier. That case has been delayed pending the outcome of the Essex trial.

Circuit Court Judge William Shore Robertson today sided with the prosecution on the question of whether a blood sample taken from Essex on the night of the crash could be admitted into evidence. The sample showed Essex, who had not been charged at the time the blood was drawn, was legally drunk, prosecutors contend.