The Federal Home Loan Mortgage Corp. (Freddie Mac) said yesterday it is ending its financing program for existing apartment buildings in the wake of loan losses that have exceeded $200 million over the past 18 months.

The Reston-based company, which buys up mortgages from banks and other lenders on the secondary mortgage market, indefinitely suspended a program that supplied funds for acquiring or refinancing existing multifamily properties. The company does not make construction loans for new apartment buildings.

Freddie Mac's decision to terminate the troubled program comes at a time when the company and other government-sponsored enterprises are fighting moves by the Bush administration and members of Congress to increase government supervision of their activities. Although the multifamily mortgages represented only a small portion of Freddie Mac's $35 billion portfolio, and the losses would be easily absorbed by a company that last year reported $437 million in profits, further losses in the program could have hurt the lobbying effort.

Although Freddie Mac is a private company, it is chartered by the federal government and its bonds are thought by investors to carry an implicit government guarantee.

The multifamily financing program has been used by numerous apartment owners to refinance short-term borrowing, typically in the form of five-, seven- and 10-year notes, for longer-term loans. Owners also have refinanced to obtain cash by taking out a new loan for the appreciated value of their properties. Those funds have then often been used to fix up older properties or acquire others.

Michael F. Coffey, Freddie Mac's senior vice president of multifamily operations, said the company halted the program because it has not made "sufficient progress toward controlling losses" in the past two quarters.

During the first six months of this year, 2.37 percent of the corporation's multifamily loans were two or more payments behind or in foreclosure. That compares to 1.95 percent at the end of last year and 0.63 percent at year-end 1985.

Coffey blamed the losses on a variety of factors, including slower real estate markets, tax law changes and specific problems at individual properties, such as poor management. The company declined to say where the problem loans are located.

Robert J. Sheehan, chief economist for the National Apartment Association, said Freddie Mac's move drives "another nail in the coffin" of the apartment industry. He noted that a number of funding sources have dried up in the past year, including the federal government's co-insurance program, in which lenders and the federal government shared the financial risks of investments in apartment buildings, and widespread participation by savings and loan associations and commercial banks.

The loan program suspension comes after Freddie Mac decided to tighten up its multifamily lending program, first in January and then in June by requiring borrowers to put more equity in their deals and forcing lenders to become better capitalized.

The Mortgage Bankers Association of America, whose members participate in the lending program, voiced dismay over Freddie Mac's announcement. Warren Lasko, executive vice president of the mortgage bankers association, called the shut-down "irresponsible," particularly because many lenders geared up to handle new Freddie Mac business when it announced the program changes.

Lasko also vowed to pursue federal legislation to force Freddie Mac to fund a minimum volume of business of about $1.5 billion a year to support financing of about 20,000 multifamily units.