Mortage interest rates to finance both new and resale house have declined about 0.5 per cent here since last October, a survey by housing economist Michael Sumichrast shows.

Effective interest rates on conventional home loans now range from about 8.75 to 9.23 per cent, which includes any mortage discount points to be paid by byuers and sellers. Sunichrast, chief economist for the National Association of Home Builders, said basic mortage interest rates now range from 8.5 to 9 per cent, depending on the amount of down payment.

However, a spokesman for area savings and loan associations, which make most of the conventional loans, pointed out that some of those thrift institutions now are making mortage loans at 8.52 per cent on a day-to-day basis if the down payment is more than 20 per cent and the term of the loan is 15 or 21 years, less than average.

Sumicharast said that his survey of 32 lending institutions indicated that there is an ample supply of mortage money in this area. Some lenders are willing to make larger loans than usual he said, and the mortage discount points (paid by sellers and/or buyers t the lender to increase the yield) have declined in recent months.

Typical effective rates on mortagage loans - with discount points included - are 8.75 per cent, with a down payments of at least 20 per cent; 9 per cent, if the down payment is 10 per cent of the house's cost, and 9.25 per cent, is the down payment in only 5 per cent. On high ratio (low down payment)loans, the borrower usualyy has to pay an additional private mortgage insurance premuim of 0.25 per cent on the total loan for 10 years.

The Sunichrast surcey showed that 60 per cent of the 32lenders contacted are offering 90 per cent loans and 40 per cent are offering 95 per cent laons. Terms run up to 30 years .

This recent trend to lower mortgage rates was confirmed by Dewitt T. Hartwell of First Federal Savings and Loan, president of hte Metroploitan Washington Savings and Loan League. He said 1977 looks good for mortgage borrowers, with the inflow of savings continuing strong and rates tending to remain at current relatively low levels.

But Hartwell cautioned buyers who might tend to wait for even lower rates that all housing prices are likely to increase by spring. Any surge of federal borrowing might tend to attract some of the "hot," or short-term money, out of passbook accounts to higher yields that would decrease the availability of mortgage funds for home buyers, he said.

Hartwell also confirmed the Sumichrast finding that more area conventional lenders now are making loans of more than $100,000 on new and sale houses if the downpayments are 20 per enct or more.

The FHA-VA mortgage interest rate ceiling, set by the secretary of Housing and Urban Development, has been at 8 per cent since early October. However, buyers have to pay one mortgage discount point (1 per cent of the mortgage amount at the time of settlement) to get financing and the seller may pay any number of point demanded by lenders to bring the yield on those federally insured or gurantied loans up to the market level. Five or six points were being charged last October, but this now down to one or two points paid by the seller.

However, spokesman for Virginia Mortgage and Investment Co., Inc., a larger volume dealer in FHA-VA mortageges, pointed out yesterday that a recent flurry in the secondary mortgage market indicated that surcharges paid by sellers or future mortgages will soon rise to two or three points.