Beating the high costs of buying, rehabilitating and renting dwellings challenges many low- and moderate income Americans in these days of inflationary economics.

The state of Maryland is helping some of its residents face that challenge by providing mortgage loans with below-market interest rates. The loans are being made to limited-income families unable to compete in the private housing market.

In addition, the state is giving financial support to some builders of rental housing who, in turn, will rent to families eligible for federal rent subsidies.

"Our primary goal is to help low and moderate-income Marylanders buy or rent houses that they can afford," said Thomas M. Cook, director of the state's Community Development Administration, which is part of the Department of Economi and Community Development.

"Since 1973, our programs have served nearly 10,0000 families; special attention has been given to the needs of senior citizens," Cook said. "During the last six months of 1977 we financed 1,541 dwelings, representing nearly half of all multi-family housing starts in the state during that period. Over the next five years we expect, at the very least, to provide housing for 30,000 Maryland families."

The use of general obligation bonds has, in part, helped make possible loans for home purchases and rehabilitation of existing houses, Cook said.A family in Allegany County's Cresaptown, for example, was one of more than 1,500 that able to finance a moderate-price dwelling, he said.

The Cresaptown couple had been looking unsuccessfully for eight years but had failed to qualify for a loan, Cook said. After their application was accepted by the Maryland home financing program, they were able to obtain a $27,000, 30-year mortgage at 7 1/4 per cent interest, he added.

Recently, a Sandy Spring couple obtained a 20-year, $11,305 loan at 6 per cent to add a new section to their existing home.

"The loan points up the value of this new approach to preserving and expanding affordable housing for limited-income Marylanders," said department secretary Herbert B. Cahan. He added that the help of local jurisdictions was enlisted in administering the program.

Loans are made in target areas designated by local jurisdictions, which Cahan described as "better informed as to local needs than we could possibly be in Annapolis."

Cook estimated that nearly 30,000 of Maryland's 1.5 million housing units need some form of rehabilition to prevent further deterioration and abandonment.

The Community Development Administration sells revenue bonds to provide construction and permanent mortgage financing to developers of rental housing as well as loans to families. So far, Cook said, the program has resulted in 5,413 dwellings.