Washington area grocery prices rose by 0.6 percent last month, even though the price consumers around the country paid for their food dropped by 0.4 percent, the government reported yesterday.

Despite the price increase in February, the rate of grocery store cost increases has slowed substantially from a year ago.

For the six months ended in February, area food prices rose at an annual rate of 6.7 percent, less than half the 13.9 percent grocery store price rise for the same period ended in February 1979.

Nevertheless the area's February increase included a sharp rise of 2.8 percent in the costs of fruits and vegetables. The largest increase in that category was 20 percent for lettuce and tomatoes an economist with the Labor Department said.

Almost as significant was a 14 percent gain here in the price of bananas, and those steep prices hikes offset decreases in other fruit and vegetable prices in the area, the government reported.

Grocery story prices of fruits and vegetables had dropped by 2.1 period during January and industry observers say the February rise demonstrates the volatility of the produce marketplace, which is effected by weather and flucturating transportating costs.

In addition to the increase in fruits and vegetables, prices of carbonated drinks other than colas, fresh whole chickens and seafood rose here, although prices dropped for eggs, beef, pork and coffee, the Labor Department said.

Prices for meats, poultry, fish and eggs dropped by 1.3 percent here in February, after rising by 1.7 percent in January. Dairy prices dropped by 0.3 percent by February after rising by 1.8 percent in January. The price of eggs dropped by 14 percent in February, the government said.

Several factors are responsible for the moderation in food prices increases in the metropolitan area, including the rapid growth of "no frills" food stores. Addition, the mild winter weather this year averted the crop damage which accompanied the harsh winter in the Middle Atlantic region last year.

Food prices have risen for three straight months, however, after dropping slightly in October and November, according to the government analysis.

Recent price freezes announced by grocery stores in the Washington area didn't affect the February figures, but they are expected to show up in the March data to be released late next month.