The Federal Home Loan Mortgage Corp. plans to ask Congress later this month for authority to sell voting stock to its customers, the nation's mortgage lenders, giving them seats on an expanded board and, in effect, turning the federally chartered company into a private corporation with government ties.

The mortgage corporation board last week gave preliminary approval to the concept, which would expand its current $430 million capital base and its ability to guarantee securities issued directly by other lenders. The corporations says that while its capital is adequate for the foreseeable future, it believes the mortgage-lending industry is going to need secondary lending funds beyond current levels.

The corporation says it intends to help "increase the competitive access of housing to the capital markets" and to "lesson the mortgage-lending industry's reliance on savings of depositors."

The FHLMC, known as Freddy Mac, is a subsidiary of the Federal Home Loan Bank Board and, because it has a federal charter, must seek congressional approval to change the nature of its operation. It purchases from primary lenders conventional mortgages that aren't backed by the government, and resells them in the capital markets in the form of participation certificates. The proposal to go private arose form recommendations of in industry advisory board organized earlier this year.

Freddy Mac wants to convert its $100 million in nonvoting common stock, currently owned by Federal Home Loan Banks, to voting common stock and to distribute additional voting stock to the home loan banks.

In a speech to the American Bankers Association in May, Freddy Mac official Edward S. Elles Jr. said the "inclination is toward issuing user stock in a certain proportion to the volume of loans the corporation purchased from an institution, or the volume of securities guaranteed by the corporation. Those who do business with us would become partial owners. . . ."

He said the stock would be dividend-bearing, "so the program would not mean higher interest rates for consumers." The corporation would lose its current tax-exempt status.

The mortgage corporation is also asking for "backstop authority" from the Treasury Department of $2.25 billion, similar to the right of the Federal National Mortgage Association, its giant partner in the secondary market, to draw on Treasury in times of emergency.

The mortgage corporation wants to expand its board from three members to nine, three of whom would continue to be members of the Federal Home Loan Bank Board, and initially to appoint the other members.

As proposed, Freddy Mac would begin guaranteeing securities -- issued directly by mortgage lenders backed by pools of conventional mortgages.

A FHLMC spokesman said that while it's too early to say how the proposal will be received on the Hill, corporation representatives have left preliminary meetings with congressional staffers "feeling good."