In addition to the mortgage "buy-downs" or subsidies being used by local home builders to attract buyers, several companies here are making additional special offers, such as mortgage arrangements to facilitate the sale of a buyer's old house.

Most purchasers of new houses are second-time buyers who must first sell their existing homes. At least two large builders are offering to make financing arrangements for both homes.

Jerold Guilbert, vice president of Edw. R. Carr & Associates Inc. in Northern Virginia, said that the firm has arranged 12 1/2 percent conventional or 12 percent VA financing for new homes built by the Carr firm in 10 communities. The Carr firm is also guaranteeing the same rate for a mortgage on the house that must be sold by the purchaser.

U.S. Home, the developer of the adult community called Heritage Harbor near Annapolis, earlier this year offered 11 1/2 percent mortgages to purchasers and 12 1/2 percent loans on the houses that the purchasers had to sell. Ron Garshag, marketing director, said the offers had stimulated sales.

Gilbert said there has been an increase in traffic since the mortgage offer was announced last weekend. The offer was made to counteract financing difficulties for resale houses that slowed the market in April. "We still think this is a good selling tool," he added.

Although Gilbert would not estimate how much the mortgage program will cost the Carr firm, he did indicate that the falling level of mortgage rates could make the financing plan more costly to Carr than it might have been if interest rates had stayed above 14 percent.

In another offer being made in Anne Arundel County, families with incomes of $23,000 to $25,000 can qualify for conventional mortgages for new town houses being built by Remarco Inc. at the Oakwood Village subdivision in Glen Burnie, said sales manager Rachel Babinec. The prices start at $61,500.

She said first-time buyers are qualifying to buy the town houses with 30-year mortgages at 12 percent and as little as 5 percent in down payment. She said that the qualifying process takes two to three weeks.

Babinec added that prospective buyers who have to break leases or take longer to buy may make a deposit of $1,000 to hold the current price of any of the houses for six months.

A total of 93 houses are planned for the 9.6-acre subdivision.