Consumers United Insurance Corp., a Washington firm, announced plans yesterday to provide up to $5 million in first-mortgage loans to low- and moderate-income housing cooperatives in the District.

The initial loan made by the company will be used to finance the renovation of a 51-unit complex at 1901-1907 15th St. NW, CUIC officials said. The company will lend the tenant association $490,000 for 21 years at 14 percent interest.

"We hope this will be the first of many loans CUIC will make to low- and moderate-income housing groups in Washington," said company president Robert F. Freeman. He noted that the funds will be distributed based on referrals from the D.C. Department of Housing and Community Development.

The company's action "is very important because it represents a commitment to stablize the District's tenant purchase program," said Marie Nahikian, a D.C. housing department official.

The District program was set up in 1979 and has helped low- and moderate-income families purchase over 35,000 units in 25 buildings, Nahikian said. "For every public dollar spent, we have invested $4 from private sources. The program wouldn't work without private support," she said.

CUIC is part of Consumers United Group, a cooperative holding company with 300 employes. "We're not like the average company trying to make money for unknown shareholders," Freeman said, explaining the decision to invest funds in mortgage loans at 14 percent interest--2 to 3 percent lower than other long-term investments.

Freeman said the company has "a social and economic conscience" and seeks only to make a "modest profit" on its investments in Washington's cooperative housing. "There isn't any catch. We have a group of people here who believe in the cooperative movement," he said.

The loan for the 15th Street complex caps a 2 1/2-year effort by the tenants to secure long-term financing for the cooperative. The group purchased the buildings in 1980 using funds from the housing department and a short-term $550,000 loan at 20 percent interest from D.C. National Bank. To help the group pay off the bank loan, the housing department later provided a 10-year $550,000 loan at one percent interest.