With interest rates down and employment up, the percentage of personal income that new homeowners spend on housing in the Washington area has dropped slightly over the past four years.

But overall, renters and owners spend more of their income on housing than they did 10 years ago, and some lenders believe the dip they have seen in average monthly mortgage payments may have more to do with people refinancing old loans than with a true decrease in the percentage of income it costs for a loan on a recent home purchase.

On a national basis, housing costs as a percentage of personal income rose rapidly during the late 1970s, as inflation pushed up housing prices and interest rates.

Chicago Title & Trust Co., which computes an average monthly mortgage payment for new home buyers in metropolitan areas, found that they went from spending 24 percent of their income for housing in 1976 to a record high of 35.5 percent in 1981.

Since then, the figure has dropped back to 30.3 percent, but many lenders say that is still too high considering the rising foreclosure rate, and area lenders say that most of the loans they write are at the top of the scale as area residents struggle with continued high housing costs.

"If a family comes here from St. Joseph, Mo., where a four-bedroom house costs $60,000, they will stretch their income to maintain that standard of living, even if the same house costs $140,000 here," said Thomas Edmunds, vice president of United Virginia Mortgage Corp., a subsidiary of United Virginia Bank. "It's very rare for us to see a loan that comes in at 20 percent of someone's income."

In the days before the rapid inflation of the late 1970s, lenders would allow home buyers to spend up to 25 percent of their gross income on their mortgage and no more than 33 percent for all their financial obligations.

Nowadays, however, lenders use 28 percent of the income as a rule of thumb for mortgages and 36 percent for all obligations, and they admit that they will stretch those rules if they believe the borrower has good prospects for salary raises or other income.

"The need for shelter is always there, regardless of how much it will cost," said Stanley Halle, a local builder and president of the Suburban Maryland Building Industry Association. "If you don't spend more of your income today, you won't be able to buy a house in this area."

Halle and other builders say that more and more working people are pairing up -- either as married couples or as friends -- so that they have two incomes to help finance a house, particularly in the expensive Washington market.

According to the National Association of Realtors, the median monthly mortgage payment on recent sales of existing homes has followed a curve similar to that found by Chicago Title & Trust. Median means half are above it and half below.

This June, a family that could afford the average new loan on a median-price home would pay $618 a month on principle and interest, or 27.5 percent of the median family income. In 1978, that average monthly mortgage payment was just $330, or 22.4 percent of family income. It peaked in 1985 at $677, or 36.3 percent of family income.

Not everybody pays that much of his or her income for a mortgage, only people who have just gotten a loan. While figures on the average monthly mortgage payment for new loans in the Washington area are not available, a 1981 housing survey done by the U.S. Census Bureau found that the Washington area median monthly housing cost -- including mortgage, utilities and real estate taxes -- was $619, or 19 percent of personal income.

The census also found that gross rent rose from 20 percent of income in 1970 to 24 percent in 1981. A recent study by the Washington Metropolitan Council of Governments found that 240,095 families in the Washington area -- most of whom are renting -- are paying more than 30 percent of their incomes on housing costs.

Several Washington area lenders said that people with high-interest mortgages dating from the early 1980s are refinancing, which could account for the slight reduction of income-to-loan percentages since 1981. Edmunds said that, in a sample of loans being processed by United Virginia Mortgage this month, nearly two-thirds of all the Federal Housing Administration and Veterans Administration loans are for refinancing.

"Because these people originally qualified for loans at much higher interest rates, they can qualify to refinance their loans at what are very low [income-to-loan] percentages," Edmunds said. "Some are as low as 8 or 9 percent, but that is not true for people taking out loans for houses they are buying right now. Those are still high, up around 33 and 34 percent."

Despite the recent drop in income-to-loan percentages, lenders report that many mortgage underwriters have begun to push for lower percentages to protect themselves against the growing national foreclosure rate -- 0.25 percent in the second quarter -- and slower housing appreciation.