A few more people across the country will be able to assume low-interest mortgages this year under a decision made yesterday by the Federal Home Loan Mortgage Corp., known as Freddie Mac.

The decision applies to persons with Freddie Mac loans who had home sales contracts on July 2, the date that Freddie Mac announced its loans no longer would be assumable at their old interest rates.

A Washington lawyer, David Kaplan, had threatened to bring a class action against Freddie Mac on behalf of three owners of Dupont Circle condominiums who were counting on using an assumption of Freddie Mac-owned mortgages to sell their condos.

Kaplan said the switch to nonassumability could have cost his clients between $10,000 and $15,000 in equity. Yesterday's decision took care of the problems of two of his clients, and Kaplan said he was not sure whether he still would bring suit on behalf of the third.

Yesterday's decision by Freddie Mac takes care of a few persons caught in the middle of trying to sell their homes, but will not be the end of efforts to get Freddie Mac to return to a policy allowing assumptions.

The National Association of Realtors is trying to persuade Freddie Mac to allow more assumptions and would consider going to court on the issue if necessary, NAR spokesmen said. In addition, there probably will be efforts in Congress to get Freddie Mac to go back to a policy of assumability, a House housing subcommittee staff aide said.

Freddie Mac is a profit-motivated congressionally chartered corporation that buys mortgages from local lenders and sells securities to investors, providing a means of getting more funds into the mortgage market.

Freddie Mac's original announcement stated that, for a mortgage it owns to be assumed at the old rate, a sale had to go to settlement by Aug. 2. Yesterday's decision extends that time to Oct. 2.