Real estate agents as well as home sellers and buyers are complaining that some lenders are taking unfair advantage of their middle-man role when people assume a low-interest mortgage owned by the Federal Home Loan Mortgage Corp. (Freddie Mac).

Local lenders who originated mortgages and then sold them to Freddie Mac continue to service them. When someone goes to assume this mortgage, they must pay whatever fees their particular originating lender charges for the service, within loose Freddie Mac guidelines, and cannot shop around for a better bargain.

Washington-area lenders now generally charge two or three points up front to transfer the mortgage from seller to buyer, a rate that agents and consumers call exorbitant for what they say is merely changing the name on the lender's books.

(A point equals 1 percent of the loan amount. So on a $100,000 mortgage a three-point assumption fee would be $3,000.)

Lenders counter that they have to do much more than that on an assumption and argue that the points are warranted by their costs, which they say are about the same for processing an assumption as for originating a mortgage. But some charge more for an assumption than an origination.

Standard Federal Savings and Loan had planned to charge five points, for example, until Freddie Mac told the S&L that was too high and forced it down to three points. On an origination of a conventional loan, Standard Federal quotes one or two points.

Freddie Mac loans have been among the few in the Washington area that could be assumed by the buyer from the seller with no increase in interest rate and, therefore, became quite valuable to both home buyers and sellers when mortgage interest rates rose to record-high levels. FHA (Federal Housing Administration) and VA (Veterans Administration) mortgages, as well as most home loans made before the late 1960s, are assumable, but most of the newer conventional mortgages -- those with the highest levels of principal left -- have clauses to prevent assumptions.

Freddie Mac last summer announced that it was changing its policy and that after Aug. 2, its loans could not be assumed. Congress later deferred this policy change until July 1983. This extension was a boon to people who had Freddie Mac loans and were planning to sell soon.

Freddie Mac allows lenders servicing its mortgages to charge "reasonable" fees on assumptions or other services, but has never defined what "reasonable" means.

Freddie Mac President Kenneth Thygerson said recently, however, that he would consider a five-point fee abusive. A press spokeswoman later said that a 2 1/2-to-three-point fee would be within the range that Freddie Mac feels is reasonable, but that lenders are expected to be able to show that their fees "bear a close relationship to the costs involved."

Thygerson said that Freddie Mac wants to hear about any exorbitant fees being charged by lenders on the corporation's loans so he can put an end to them.

When quoted the five-point figure by Standard Federal, real estate agents reportedly reacted resentfully, since it would substantially reduce the value of the assumption feature of Freddie Mac loans.

A Standard Federal official, who refused to be identified, said that in the end the S&L never charged anyone five points, though it had informed real estate brokers that it would.

"I've been in the business for 33 years . . . and it [the assumption fee level] is the highest I've ever seen," said William Sikes, a Falls Church broker. Lenders started charging for assumptions in the 1950s, then went to a small, flat fee and until recently typically charged one point, Sikes said.

Lenders "are just seeing an opportunity to pick up some money," Sikes added.

Asked how Standard Federal justified its three-point charge, the Standard Federal official at first replied, "Why do I have to justify our costs?" When it was pointed out that Freddie Mac requires this on its mortgages, the official said that he thought a five-point fee could have been justified to Freddie Mac but that, "to preserve our good relationship with Freddie Mac," the five-point charge was withdrawn.