The supply of surplus food stored at taxpayer expense has been reduced so much that the government will cut donations to food banks and soup kitchens, officials said yesterday.

For the 12 months that began Oct. 1, 210 million pounds of free cheese will be available, compared with 420 million pounds in 1986-87; 48 million pounds of nonfat dry milk, instead of 96 million; 48 million pounds of honey, instead of 76 million, and 90 million pounds of rice, instead of 180 million.

Federal policies and decisions by dairy farmers have slowed, at least temporarily, the milk-production surges of the early 1980s that led to huge government inventories of butter, cheese and powdered milk.

Diane J. Durant of the Agriculture Department's Food and Nutrition Service said the reduction means that the commodities will begin to run out by April because the food is being given to states at the previous monthly rates, she said.

Durant cautioned that the projections are tentative and that some authorities cite a possibility that the department will replenish its dairy surplus inventories if farmers continue to increase milk production.

"The inventories are in flux," she said in an interview. "Dairy policy succeeded in reducing the {surplus} inventories . . . and we're not sure where that's going to be headed in the next year."

Department officials expect to have a better idea of what may happen by January, Durant said. Meanwhile, the agency must notify the states, which delegate food distribution to local sponsors such as food banks, of levels that they can expect. "This is tentative, and it may change dramatically," she said.

Other surplus commodities to be distributed at last year's level, she said, include 48 million pounds of corn meal, 72 million pounds of butter and 144 million pounds of flour.

According to the department's Commodity Credit Corp., which controls the government-owned surpluses, uncommitted inventories Sept. 30 included 82.3 million pounds of butter, down from 193.8 million pounds a year earlier; 98.5 million pounds of cheese, down from 558.7 million, and 63.1 million pounds of nonfat dry milk, down from 696.6 million.

The government also donates dairy products and other commodities to schools, military forces, prisons and other institutions. Foreign aid programs and sales abroad also are outlets.

The department has operated some type of commodity distribution for many years, but operations were expanded in the early 1980s as dairy surpluses soared and the number of hungry people increased.

Between 15 million and 18 million people have received free food monthly under the programs, according to USDA estimates.