Costs of buying and maintaining houses and apartment buildings increased 2.1 percent during the last two months in the Washington area, contributing to an overall consumer prices rise of 1.5 percent, the Labor Department reported yesterday.

But real estate executives and mortgage loan officers at area savings and loan associations said they saw no letuup in homebuying despite increasing proces and interest rates that are near record levels.

"The reason we are still selling homes is because there are enough people with incomes that have more than kept pace with the rise in prices," said Kenneth J. Luchs, copartner of Shannon and Luchs. He estimated that area home prices now average between $70,000 and $80,000.

Increases in mortgage and interest rate cost, utility bills, rent and home furniture prices all contributed to the higher cost of living in the period from mid-July to mid-September, more than offsetting a 0.9 percent decline in grocery store prices.

Restaurant bills also rose by 1.1 percent and apparel prices increased by an abnormally steep 4.3 percent during the months.

Washingtonians have the second highest monthly housing expenses among the nation's large metropolitan centers, trailing only San Francisco, and yesterday's government report indicated no letup in the housing-cost spiral.

For example, officers of the Federal National Mortgage Association, a key source of home mortgage funds, are forecasting no significant decline in interest rates for the next year. The current mortgage rate level of 10 percent is a "bargain" compared with a 12 to 14 percent annual appreciation in home values, said FNMA Chairman Oakley Hunter. (See story, Page E1.)

Interstate Federal Savings & Loan loan officer Herbert Haller attributed the high housing prices to buyers' willingness to pay them.

"The buyer increases the prices because they're willing to pay them and the sellers know this and they say, 'Let's take advantage of it," Haller said. "A man who has been in his house for a few years is just flabbergasted when the agent tells him how much he can sell his house for."

Haller said that because of the higher prices, Interstate's average mortgage loan now is $60,000. Perpetual Federal loan officer James R. Carlin said his institution's average is $100,000.

Haller and Carlin said Savings and Loan associations had increased mortgage interest rates because customers are taking money out of savings accounts and putting their money in investments with a higher interest yield, such as certificates on which the association must pay more.

According to the Metropolitan Washington Savings and Loan League, passbook accounts (interest ceiling of 5 1/4 percent) declined $154 million at 20 D.C. and Maryland institutions over the past year. Deposits that require higher interest payments rose $351 miillion for the area S&Ls, the largest source of home mortgage money.

Other cost-of-living increases here roughly parallel, but are slightly higher than nationwide averages.

The two-month increase of 1.5 percent overall compares with 1.3 percent for all large cities, while the increase in prices over the past 12 months was 8.5 percent compared with 8.3 percent for all cities.

Stated another way, the current cost of living index here stands at 200.8 percent of its 1967 average: selection of goods and services that cost $10 11 years ago now has more than doubled to $20.08. This is a difference of 15 cents from the national index of 199.3, which would indicate an outlay of $19.93 today to buy goods and services that cost $10 11 years ago.

Among metropolitan areas in which the cost of living rose faster over the 11-year period are Baltimore, Denver, Cincinnati, Portland, Ore., San Diego and Seattle, according to Labor Department figures.

Home purchase prices, in particular, haven been climbing steadily here - at a rate of 20 percent a year for some properties over the past five years.

Natural gas and electricity bills have jumped 15 percent in the past 12 months and the costs of household furnishing have increased 9 percent.

And, since overall housing bills account for the largest share of the average area consumer's spending here (47 cents of every dollar), price increases in the housing sector have a major impact on the total consumer price index. Transportation accounts for 17.4 cents and food, 17.3 cents, of the consumer dollar here, while apparel accounts for 5.8 cents.

"Most people familiar with real estate aren't surprised but people who aare in their own homes drop their teeth at the (10 percent) mortgage interest rate," said Claudia Van Veen, the real estate sales person at a new upper Northwest town house development of $135,000 homes. This is because many of them have 4 or 5 percent mortgages, she explained.

"People are setting their sights lower," said Donald Snider of Snider Bros. "Before, they wanted a detached house as starter, but now they are settling for a town house just to get on the bandwagon.

"People are still buying," said Katherine Peck, president of Hugh T. Peck real estate company. "We are 30 percent ahead of last year's sales.