The proposal for an Adjustable Rate Rider should preempt state law and make adjustable rate mortgages assumable at the bank's discretion and at any rate not above that charged on new ARMs. In practice, said a spokesman, banks usually adjust the rate on an assumed Adjustable Rate Rider about halfway between the old and new rates.

The comptroller's office said the proposal is aimed at giving banks flexibility in lending, while the Federal Home Loan Bank Board has come out against savings and loans allowing mortgages to be assumed.

In another action, the Federal National Mortgage Association notified lenders that it would not enforce its new policy against buying assumable mortgages on Adjustable Rate Rider, scheduled to go into effect Oct. 1, because a number of states permit these assumptions.

Fannie Mae had intended to stop buying mortgages that could be assumed because prolonging the life of low-interest mortgages in times of rising interest rates cuts into its profits. However, as the result of several court cases and consumer protests, 11 states have legalized assumption by prohibiting lenders from including "due-on-sale" clauses in mortgage contracts. (Such a clause means the balance of the mortgage is due when the house is sold and a new buyer may not continue to pay off the old mortgage.)

Fannie Mae said it would delay enforcement of due-on-sale clauses until some unspecified date. Meanwhile, a spokesman said, it will consider whether to put a surcharge on assumable mortgages or allow a lender to call them due after a certain number of years.

The Federal Home Loan Mortgage Corp. is taking two more steps toward building a comprehensive program to encourage lenders to make more adjustable-rate mortgages. Edwin J. Gray, chairman of the Federal Home Loan Bank Board, announced the two new programs in San Francisco at last week's western secondary mortgage market conference, sponsored by the California League of Savings Institutions.

Mr. Gray also announced record second-quarter earnings for Freddie Mac, as the corporation is known. Freddie Mac's sole shareholder is the Bank Board, and Mr. Gray is also Freddie Mac's chairman.

Although Freddie Mac has only been buying adjustable-rate mortgages or ARMs for three months, Mr. Gray said the instruments are one of its top priorities. Under this new program, Freddie Mac buys 30-year term mortgages with rates and payments that adjust either every three or five years, based on the three- and five-year Treasury indexes.