During the past decade supermarket chains have been deserting the inner cities in alarming numbers, leaving residents without cars few or no alternatives to expensive convenience stores. The number of markets in urban areas has declined between 28 and 50 percent in Boston, Washington and Chicago, for example.

Now a manual on how inner cities can maintain or bring back food markets has been put together by the Community Nutrition Institute. Using six case studies, including Santoni's Market in Southeast Baltimore, the authors offer a practical guide for establishing food co-ops, farmers' markets and independently operated supermarkets.

Among the hints for saving a community store are limiting food assortment to 1,000 or so staple items and selling products that cater directly to neighborhood needs. Most people who buy with food stamps don't need appliance and camera equipment counters in their markets.

Also suggested are Sunday hours, wine and beer sales, minibus transportation and child care centers at the market for shopping mothers. The community is urged to lobby the local government to get a low cost lease on adjacent city-owned property that could be used as a parking lot, and for resurfaced sidewalks and high powered street lights where needed. Citizen crime patrols and community clean-up campaigns are also advised.

The manual describes a joint venture takeover in which a community organization leases the troubled store from the supermarket owners. It pays the supermarket firm a management fee to operate it. It relates how the six communities mentioned put together different types of financial packages, including both private and government funds. It stresses the necessity of a professional feasibility study.

The guide, entitled "Food marketing Alternatives For the Inner City," is available from CNI, Consumer Division, 1146 19th St. N.W., Washington, D.C. 20036. The telephone number is 833-1730.