The Virginia Alcoholic Beverage Control Commission, Whose numerous regulation cover everything from who may buy alcohol in the state to the maximum size of a restaurant table, finally is dropping its rule that mental patients may not buy beer, wine or whiskey.

The prohibition was repealed in the 1979 General Assembly, but the commission somehow neglected to follow through and remove it from its 68-page book of regulations.

While the that and other changes are being considered at "open-door" meetings around the state, the commission already has changed the forbidding signs it posts in every ABC store. The signs used to read:

"The following persons ARE FORBIDDEN to make purchases in this store:

"1.Those under 21 years of age.

"2. Those interdicted.

"3. Those intoxicated.

"4. Those under the supervision or control of any state hospital (mental paitents)."

That last restriction has been painted over; in its place the seal of the Commonwealth of Virginia.

"The change had been sought as far back as 1974 by the Department of Mental Health and Mental Retardation," said T. Rodman Layman, ABC chairman. "The head of the department then, Dr. Williams Allerton, thought it most inappropriate. He said it stigmatized mental patients as second-class citizens."

Repeated attempts to remove the prohibition failed in the General Assembly until last year, when Del. Franklin P. Hall (D-Richmond) succeeded in getting it rescinded.

Lynn Schultz-Writtsel, acting director of public information and education at the National Metal Health Association in Rosslyn, said such restrictions on mental patients, many of whom often are released to visit their families, are not unusual. "In the District, when you apply for a driver's license, you have to check a box on the form if you have been a (mental) patient or are under treatment."

As for the change in Virginia, she said, "I think it's very positive action. The old law was like not selling firewater to Indians."

In another liberalization of ABC rules, restaurants now may count sandwiches as meals in calculating their food sales. Further, food now must account for only 45 percent of total sales, and receipts from sale of drinks now may total as much as 55 percent. Under the old ratio, food sales had to account for 50 percent of a restaurant licensee's gross income, and sandwiches could not be counted as meals.

The purpose of the food-liquor ratio was to keep the "saloon atmosphere" out of Virginia, according to ABC officials.

Some observers questioned whether the former ban observers questioned whether the former effective.Dr. James B. Funkhouse, who was deputy commissioner of mental health until his retirement last fall, said, "I've been in liquor stores many times in the last 40 years, and no one ever asked me if I was a mental patient on leave."