A contingent of earnest adults and another of impassioned students turned out last week to argue opposite causes before a Virginia General Assembly subcommittee that is studying a proposal to change the drinking age for beer from 18 to 20 years.

Approximately 10 school and county officials, principles and parents expressed support for raising the legal age to drink beer during the subcommitttee's public hearing Thursday at Fairfax County's Massey Building.

But some 12 Fairfax County high school students dominated the 2 1/2 hour hearing with repeated entreaties that the proposed law would be discriminatory, unenforceable and ineffective.

The hearing was the first in a series to be held around the state through October by the General laws Subcommittee on Virginia's Alcoholic Beverage Control. The four-member subcommittee is seeking citizen reaction to a proposed bill introduced by Del. Warren Barry (R-Fairfax) to change the drinking age for beer to 20.

A similar bill was killed by a 12-7 vote by the full 20-member General Laws Committee in 1976. The bill proposed by Barry, who is serving on the subcommittee, is one of three under consideration by the General Laws Committee that would raise the legal age for drinking beer. Another bill would raise it to 19 and a third bill would raise it to 21, the same age required to buy wine and liquor.

Barry, who explained that his interest in the bill resulted from problems with alcohol among his three sons, said the intent of his bill is to raise the age to 19.

"But the General Assembly works like a business. You have to allow some room for concessions," he said.

The main purpose of the bill - and one wholly supported by county authorities including County Board of Supervisors Chairman John F. Herrity and School Superintendent S. John Davis - is to reduce the accessibility of alcohol among high school students.

Testimony by Herrity, Davis and other adults at the hearing pointed out that it is all too common for 18-year-olds, many still high school seniors, to buy beer for their younger friends.

They claimed the lower drinking age, established by the General Assembly in 1974, has contributed to a significant increase in teen-age automobile accidents and traffic arrests. It also has interfered with extracurricular school activities, such as games and dances, causing some of the activities to be curtailed, they said.

The students, on the other hand, claimed that it is only a "small minority" of students that abuse alcohol and said the General Assembly would be making a majority of responsible students suffer for the violations of a smaller group by raising the age.

Herrity ticked off a battery of police statistics to justify the proposed law. He said that there was a 400 percent increase in the number of teen-agers under 18 arrested for drunk driving in the 18-month period following the lowering of the drinking age in 1974. In the same period all arrests for drunk driving increased only 80 percent, he said.

Davis and two school principals at the hearing said they have been "encountering problems we never have had before," with teen-age drinking during games, field trips and other school activities.

Barry, who sat at the subcommittee heariing with only one other member, L. Ray Ashworth (D-Sussex), told Davis he had heard of cases in Northern Virginia where school activities had turned into "drunken orgies" and that some students had to be revived in order for parents to take them home.

Davis indicated he was aware of teh problems and said some school activities have had to be eliminated and school authorities have had to frisk students before they entered school functions.

Chuck William, 18, a Chantilly High School senior and former member of the county's Students Advisory Committee to the school board, said he drinks beer, but had never been at a "drunken orgy at school."

He said he is registered voter and considered and adult by law, that he is eligible for the draft, responsible for paying taxes, allowed to enter contracts and "could even face a long term prison sentence.

"It would be discriminatory to take away my right to drink beer," Williams said , echoing the collective sentiments of students at the hearing. "Besides, the law would be unenforceable because kids can go to Georgetown to buy beer if they're 18. You would only be encouraging them to make longer drives."

He told the subcommittee he was "insulted" by its "stereotyping of young people. . . it's but a small number who buy beer for kids under age."

Barry responded by saying he was sorry Williams was insulted by his proposed bill, but that "right can be taken away from people when they are not responsible."

He said by William's terms, young people were already discriminated against in the law by not being allowed to buy liquor and wine until they are 21.

"Why can't you buy hard liquor Barry asked Williams, who responded, "Because I haven't gotten the General Assembly to legislate that through yet."