Washington area food prices increased by more than 7 percent in the last three months, sending more lowincome residents of the District to city government agencies in search of fihancial help and nutritional advice.

According to the Labor Department, area food costs soared 2.5 percent last month after a 2.6 percent increase in January and a 1.9 percent gain during December, mostly because of ballooning prices of meats, fruits and vegetables.

Although area figures for the last three months add up to an annual rate of increase exceeding 25 percent, government and food industry economists pointed out that prices normally are much higher during the winter months.

But beef price increases are not expected to moderate and area food costs could rise as much as 15 percent this year, based on the data in yesterday's report.

"That's staggering," said George Grier, a Washington consultant who is working on studies about living costs for the poor. "For people at the lower end of the income scale, that's an insufferable thing when added to energy prices that are rising [at a reat] twice the general [price] index, in addition to housing costs."

Grocery store price increases have contributed to a sharp rise in the number of District residents who have sought assistance in obtaining food. Since last July, about 5,000 low-income persons have joined a supplemental food program of the Department of Human Resources. Altogether, more than 14,000 city residents now are receiving free distributions of food at 11 city centers.

Natalie Zetter, a public health nutritionist on DHR's staff, said yesterday that since limited incomes "can go only so far," there is increased concern that less affluent city residents are not getting adequate protein in their diets.

And a supermarket official, Giant Food Inc. consumer affairs specialist Odonna Mathews, had some advice for customers yesterday that was unusual for a retailer. "Try to avoid impulse buying," she said.

Both Mathews and Zetter emphasized that proper combinations of vegetables with smaller amounts of meat could help stretch food dollars. The use of noodles, rice and pasta also was recommended.

Average consumers spend one-fourth of their food budget for meat -- 60 percent of which normally is beef, the price of which has been increasing at a higher rate than those of most food items.

According to statistics from the government, meat, poultry, fish and egg prices in the metropolitan area rose 3.8 percent from January to February after a 2.1 percent rise the previous month.

Ground beef and chuck roast prices posted the largest increases. But prices also rose for most pork items, fish, seafood and poultry. Regular hamburger at area Safeway stores now costs $1.59 a pound compared with 99 cents a year ago.

Safeway, introduced at its area stores during the past month a new "patty mix" that contains some beef plus vegetable protein and is selling this week for $1.29 a pound. "It's selling very well," said Tony Statom, a Safeway spokesman.

Prices of fresh fruits and vegetables also rose sharply from January to February, but the 4.1 percent rate of increase was down substantially from a 7.3 percent rise the previous month. Lettuce, which was being priced at about a dollar a head several weeks ago, is now two heads for 89 cents at both Giant and Safeway, the area's two biggest food chains.

Among other food items last month, cereal and bakery products rose 1.3 percent and dairy products were up 0.3 percent.Labor Department officials said prices declined for carbonated drinks other than cola, and for oranges, ham, bread and coffee.

The overall 2.5 percent monthly increase here was higher than the 2.2 percent average food price increase in all U.S. cities during February. For all of 1978, area grocery stores prices rose 10.1 percent. Food prices are reported monthly for this area while an overall local consumer price index is published every two months.

"It's not easy, that's for sure," said Mathews, of Giant Food, in discussing how consumers can stretch food dollars. She said her firm had started two programs recently to help -- weekly recipes in newspaper advertisements that use food items on sale that week, and a biweekly "Eaters' Almanac" available in area stores, with information on different food groups and suggestions for cheaper substitutions for some items.

This week, for example, Giant siggests baked fish fillets, with porgies selling for as low as 69 cent a pound ($1.03 for prepackaged) and croakers at 79 cents a pound ($1.22 prepacked).

Zetter, the city government nutritionist, said that city residents must show extra financial need as well as helath reasons to participate in the supplemental food program. Typical residents involved are pregnant women, infants, children up to 6 years old and elderly persons.

DHR has stepped up its educational programs in recent months, probably acccounting for some of the recent 5,000 increase in the number of persons who now get free evaporated milk, canned juice, vegetables, canned beef, peanut butter, baby formula and dried potato flakes.

D.C. residents who have inquiries about the program or who would like to invite city nutritionists and food technicians to organization or community meetings, should telephone 637-6800. Zetter said DHR staff persons speak on buying habits and consumer concerns as well as natrition and substitute foods.