Virginia Gov. John N. Dalton has exercised his first veto of the 1981 legislative session on a controversial automobile negligence measure sponsored by a lawyer-legislator who specializes in personal injury accident cases.

The bill, introduced by Democratic Del. George Allen of Richmond, would have created a legal presumption that any driver whose car was in an accident after leaving the roadway was guilty of negligence.

"The end result of this legislation in my opinion would be increased monetary judgments, which would translate into higher automobile insurance rates for the consumers of the commonwealth," said Dalton, himself a lawyer, in his veto message.

Allen said today he does not plan to seek the two-thirds vote of each house necessary to override the governor's veto. Allen's measure squeaked through the Senate on a narrow 20-to-15 vote last month.

Legislative critics had called the bill "the most crass piece of legislation" seen in Richmond in years, and charged that Allen, who is known here as the "King of Torts," had introduced it as a means of "feathering his nest." Supporters had countered that many of Allen's critics were themselves caught in a conflict of interest, because several of them are lawyers who represent the insurance industry.

Allen had conceded that the bill had the potential to benefit his law firm of Allen, Allen, Allen and Allen, a firm that represents plaintiffs in accident cases and is one of the largest of its kind in the state. But he insisted that there was nothing improper in his introducing the legislation, arguing that his expertise in the area made him well qualified to correct what he saw as an inequity in state law.

In other legislative action, the Virginia Senate today sent Dalton a compromise measure that will raise the state's legal age for off-premises beer purchasers to 19 but leave intact the current limit of 18 for bar and restaurant beer drinkers. Dalton is expected to sign the measure.

Bill sponsor Del. Warren Barry (R-Fairfax) who had promoted the measure as a way to reduce traffic deaths among teen-agers, called the bill a "step in the right direction" and said he hoped it could eventually lead to legislation that would raise the legal drinking age to 21.

Earlier proposals by Barry to raise the limit to 21 were torpedoed by House Majority Leader Thomas W. Moss Jr. of Norfolk, who has represented several restaurants and bars before the state's Alcoholic Beverage Commission.