A steep rise in the cost of beef helped increase Washington food prices by an unusually high 2.2 percent between January and February - almost double the national increase - according to the U.S. Department of Labor.

The latest increase followed a 1.2 percent rise between December and January and pushed food prices here up to more than 11 percent above what they were a year ago.

Although food prices here are now climbing faster this year than last, Jeffrey Thomas of the Bureau of Labor Statistics cautioned that "there is no way to say it's a trend" because food prices are traditionally unpredictable.

Unlike national food prices, the Washington area statistics are not adjusted for seasonal fluctuations. In addition, Thomas said, it is difficult to gauge this year's increases against those for similar periods last year because of some changes in the way consumer prices are being calculated.

However, Thomas said the recent price increases here are still "fairly high" compared with the old statistics, which were based on the buying habits of a smaller portion of the population. A separate government forecast also has revised upward projections for further food price increases this year.

Nationally, grocery store prices increased by 1.2 percent in both January and February, with about three-quarters of the increase last month attributed to higher meat and poultry prices. Beef prices rose 4.1 percent in February, following 2 percent increases in each of the previous three months.

Ernest Moore, a spokesman for Safeway, said his company's wholesale beef prices increased as much as $4.50 a hundredweight (each 100 pounds) between January and February, mostly because of lower beef production. Moore said there has been a smaller herd available for slaughter. He also cited adverse weather conditions as a factor contributing to higher feed costs.

Beef wasn't the only item on supermarket shelves with higher prices here last month. Moore said cold weather in Florida had forced Safeway to bring lettuce in from California instead, at a price up to $2 a carton higher. Apples from the Pacific Northwest also were more expensive because of increased export demands. Heavy rains in California reduced crops there and forced some other produce prices higher.

Government statistics showed that, in addition to beef, prices rose significantly for all fresh fruits and vegetables, eggs, lamb and pork. Lower prices for bread, processed vegetables and cola drinks did not offset the sharp increases.

A spokesman for Giant, Barry F. Scher, said last month's food price increase here "simply reflected the tremendous farm products wholesale price increases of January and February."

In a new food price forecast, Department of Agriculture economists yesterday revised upward to a range of 6 percent to 8 percent their projection for retail food price increases over 1977. Earlier, USDA had predicted increases in a range of 4 percent to 6 percent.

Three reasons were cited by USDA for the upward revision: food prices in the early months of 1978 have been greater than expected; pork production is expected to be less than expected, and inflation in the general economy has been greater than previous forecasts.

If yesterday's forecast is accurate, food price inflation could top the 6.3 percent national average increase last year, which would be the most rapid rate of increase since 1975, when prices rose 8.5 percent.

Congress currently is considering an emergency farm bill that government economists have said could add another 2 percent to projected food price increases.

Washington area food prices are expected to follow national trends, in general, although several factors have been cited for food price increases here that already exceed national averages.

Scher, the spokesman for Giant, has attributed higher prices in the Washington area to greater cost of doing business. For example, more than 19 cents of each dollar spent by customers of Giant pays for labor wages and benefits, compared with a U.S. food chain average of under 15 cents.

In addition, more affluent Washington area food buyers purchase more beef than consumers in most other markets, supermarket spokesmen said.