Thousands of military families could be forced to pay 10 percent more for food, and have fewer commissaries to shop at under a cost-cutting plan that has been sent to Capitol Hill.

The General Accounting Office, financial watchdog of the Congress, says taxpayers would save millions of dollars if subsidies to military food stores are cut, and unneeded commissaries in and around big cities are closed.

Commissaries are a vital part of life for the 58,000 active duty and 20,000 retired military here. There are nine commissaries open here to military and dependents. Although many shoppers argue that the stores are no bargain, Defense Department data says that overall savings to commissary shoppers amount to 25 percent compared to prices they would pay in regular supermarkets.

Despite user complaints that commissaries are not bargain centers, are crowded and have inferior goods, they recorded $3 billion in sales last year, making them one of the nation's ten top grocery operations.

Commissary shoppers -- who include some foreign diplomats and military aides based here -- saved an estimated $840 million last year over prices they would have paid at Safeway, Giant and other large chains, according to the GAO report.

The congressional auditing agency said commissary operations in 1978 were subsidized to the tune of more than half a billion dollars. That included $394 million in appropriations to Army, Navy and Air Force budgets and another $150 million saved because the commissaries are exempt from federal, state and local taxes including sales taxes.

Congressional appropriations, according to the GAO recommendation, ought to be reduced, commissaries should be better managed and many big city commissaries should be shut down.

Original purpose of the commissaries, which are nearly as old as the Republic itself, was to provide reasonably priced food to chronically underpaid military families. Congress authorized them in "remote" areas where food stores were not convenient.

GAO did not target any commissaries for closing (there are nearly 400 in the world). But metro Washington could be a prime target.There are 122 Safeway stores, 35 A & P and 120 Giant stores here in addition to other food outlets. Those food chains would love to capture the military market dollar, and local jurisdictions drool over the prospect of added revenue from sales tax money that now eludes them.

If commissary patrons were required to assume subsidy costs in the form of higher prices, GAO and Defense estimate the savings over regular supermarket prices would be reduced to between 11 and 15 percent.

Cutting military benefits always is a controversial and explosive situation. And recruiting problems of the all-volunteer military make them even more complicated. Whether Congress will tackle them in this year of chilled Soviet relations, the Iranian situation and the 1980 elections remains to be seen.