With the number of supermarkets in Washington reduced by more than half since 1968, Mayor Marion Barry said last night that he has told city planning officials to put a priority on the development of new food outlets in city neighborhoods.

Barry told a meeting of about 25 persons concerned with consumer protection that his administraton will use federal and city funds, tax incentives and zoning powers to construct stores and attract both chain and independent operators.

Since 1968, the year Washington was torn by rioting, the number of supermarkets in the city has declined from 91 to 42, the mayor said, with an additional closing now palnned by the city's largest operator, Safeway.

Because of high land costs in the city, Barry said he supports mixed-use zoning, in which supermarkets would be located on ground floors of multistory buildings.

His statement on food marketing was included in a speech that largely repeated promises he made on consumer protection issues during last year's mayoral campaign.

The mayor also reiterated a proposal he made to the City Council last week for raising the maximum interest rate in the city to encourage small loan firms to locate inside the city, instead of clustering in Maryland just outside the District line.

Barry said he would raise the maximum 8 percent small loan rate, prhaps to about the 18 percent premitted on credit cards. Small loan firms in Maryland can charge as much as about 33 percent on a one-year, $300 loan.

Marie Dias, a mayoral aide, said she assembled yesterday's group to meet with the mayor based on their interest in comsumer protection matters.

Included were some of the seven members of the 11-member Advisory Committee to the D.C. Office of Consumer Protection who resigned in December protesting alleged mismanagement by the director of the city's Consumer Protection Office, Bettie J. Robinson.

Robinson was not invited to last night's meeting and Barry said later that her absence does not mean either that she will be kept in that post or be removed.

Ana Aldama, who was chairwoman of the advisory committee but submitted her resignation to former mayor Walter E. Washington, said Barry voiced sound sentments but did not spell out a timetable for reforms.