The news last week that the "best bet" for "consistently low" area liquor prices is in the 20 stores run by the Montgomery County Department of Liquor Control, it turns out, needs some qualifying.

Although Robert Krughoff, the publisher of Washington Consumers' Checkbook that released the survey, stands by its accuracy so far as the data presented, he now cautions:

"The survey focused on 750 milliliter ('fifth') size liquor bottles; the results might be different for 1.75 liter ('half-gallon') sizes, which have been gaining an increasing share of the market since 1978, when we first began this survey, particularly for the higher-income consumers."

In other words, the District -- long considered the source of best liquor buys -- may still be a good place to buy, acknowledges Krughoff, if you tend to buy in "half-gallon" sizes.

The survey itself suggests consumers "can save by buying large bottles. The savings in buying 1.75 liters instead of 750 milliliters generally run 5 to 15 percent, but sometimes are larger."

Checkbook, says Krughoff, now plans to expand the study to include the larger-size liquor quantities.

"We first looked at liquor store prices in 1978," Krughoff writes in the survey. "At that time we surveyed every store in the Washington area (more than 700 stores), and we checked the prices on 10 items at each store."

Results of the 1978 study were not published but were used as a basis for the current survey, taken in July of this year and appearing in the September issue of PriceFighter, the newsletter that goes to the approximately 27,000 Checkbook subscribers.

The current survey included: 25 stores each from Prince George's County and the District (that had ranked least expensive in 1978), the Montgomery County and Virginia Alcoholic Beverage Commission outlets, a random sampling of 30 stores each from the District and Prince George's, plus six stores in Columbia (not surveyed before).

"There may be other stores that are low-priced now," Krughoff writes, "but were not low-priced or were not even in business in 1978. We did not include them because we were interested in stores that have a long-standing record of low prices."

The July survey indicated prices -- of specific-size purchases -- at the Montgomery County stores averaged 13 percent less than the average prices at outlets in Prince George's and the District.

Virginia ABC stores, while higher than Montgomery County's, were below those of all 55 outlets surveyed in the District and all but a few of the 55 checked in Prince George's.

Only one store in the survey, B.K. Miller in Prince George's, averaged lower prices than the Montgomery County stores.

The 10 items priced at each store, along with their container sizes, were: J&B Scotch (750 ml.); Old Grandad's Bourbon (750 ml.); Budweiser beer (6-pack, 12-ounce cans); Gordon's gin (750 ml.); Almaden Mountain White Chablis wine (1.5 liter); Seagram's 7 blend (750 ml.); Smirnoff vodka (750 ml.); Bacardi rum (750 ml.); Heineken beer (6-pack, 12-ounce bottles), and Bolla Soave wine (1.5 liter).

The best Budweiser prices were found in drugstores and supermarkets. The lowest metropolitan prices, including tax: Basics ($2.59) and Memco ($2.66) in Virginia.

Stores with the lowest average prices (Checkbook gives a "price index figure," which is an adjusted mean price of the items checked): District

Family Liquor, H Street NE ($9.69); Central Liquor, 9th Street NW ($9.83); Washington Wine & Liquor, E Street NW ($9.83). Prince George's County

B.K. Miller, Clinton ($9.18); Veteran's, Beltsville ($9.28); Astor Home, Laurel ($9.47). Columbia

Oakland Mills Liquor, Oakland Mills Village Center ($9.95, 7 percent lower than the average prices in other Columbia stores).

Average prices in the District stores ($10.63), Prince George's ($10.64) and Columbia ($10.68) were comparable, but above Montgomery County ($9.20) and Virginia ($9.59) averages.

Prices on the selected items, even among outlets with the lowest mean prices, varied considerably. J&B Scotch, for example, listed at $9.12 at B.K. Miller, ran $11.65 at Addy Bassin's MacArthur (Northwest D.C.). Old Grandad's Bourbon (86 proof) was $6.81 at Hampton Discount Liquors Inc. (Capitol Heights) and $9.11 at Jefferson Liquor Store (Northwest).