Montgomery County Executive Charles W. Gilchrist yesterday authorized a ban on the sale of Russian vodka in the county's 21 liquor stores, an action taken, he said, to protest the Soviet downing of a South Korean civilian airliner.

His action came a day after Virginia Gov. Charles S. Robb authorized removal of Russian vodka from the shelves of state-run liquor stores.

Six other states have also made the same move, according to a Gilchrist spokesman.

"We realize this move is more symbolic than punitive toward the Soviet Union," Gilchrist said, "but it is a statement that Montgomery County can and should make in its role as a liquor retailer."

The county's Department of Liquor Control is also canceling a current order of 112 cases of Stolichnaya vodka immediately, according to Gilchrist's spokesman Charles Maier. Maier said there are about 240 cases of the popular vodka already in stock at the stores, with an estimated value of $25,000.

These cases will be stored away, and signs will be posted advising customers of the county action.

Gilchrist also authorized a ban on the weekend special sales of Stolichnaya vodka in 1979 after the Soviet invasion of Afghanistan.