American home buyers, including a growing majority of households with two incomes, are committing more than a quarter of their earnings to purchasing homes, a figure that has risen substantially over the last few years.

The price of homes and the monthly cost of mortgages rose more than a third between 1977 and 1979. And the number of first-time home buyers was cut in half during the same period.

These grim statistics emerge from a report entitled "Homeownership: Coping With Inflation" released yesterday by the .S. League of Savings Associations. The data came from more than 14,000 conventional mortgage loans on single-family homes made in the second quarter of 1979 and selected from 350 savings and loan associations across the country.

Nationwide, the median sales price of a house last year was $58,000, up from $44,000 in 1977 when the league did its first such study. The median monthly payment for mortgage, taxes, insurance and utilities rose from $400 to $550. (Median is the midpoint; half of those surveyed paid more and half less.)

Once again metropolitan Washington was rated the third most expensive city, after San Francisco and Los Angeles, for home buyers in 20 cities studied. The median sales price here in 1979 was $76,000, up 12 percent from $68,000 two years earlier. The median monthly expense was listed at $752, up 30 percent from $578. Nearly three quarters (73 percent) of the home buyers had monthly carrying charges of more than $600, compared with one third (36 percent) two years before. Almost all of the difference resulted from increased mortgage interest rates and a tendency on the part of repurchasers to take out the maximum mortgage allowed.

During those two years the median income of Washington-area buyers rose 13 percent, from $32,718 to $36,993. But the big difference was in how it was earned. Almost half again as many households (63 percent, compared with 45 percent) last year depended to some degree on the income of a second wage earner. And half (51 percent), up from 36 percent two years ago, spent more than a quarter of their combined income on housing.

The number of singles, either as individuals or as unmarried couples, buying huses doubled from 21 to 41 percent. Due to changes in lifestyle, as well as rising prices, 45 percent of the buyers purchased condominiums. That is three times the number of condo buyers in other big cities and four times the national average.

The two-income household has become the norm (54 percent) among home buyers. In 1977, the second wage earner contributed less than 10 percent of the combined income in a majority of households. Today in almost half of the households (48 percent), the other breadwinner contributes between a fifth and a half of the income.

The rise in housing costs, together with the recognition of the value of real estate as an investment, has pushed more home buyers to make sacrifices and leader to go along. The old rule of thumb of 25 percent as a ceiling is gone.

The league study found that half of the home buyers were spending more than 24 percent of their monthly incomes in housing. The greatest increase was in the category of those spending 30 percent or more, up from 14.5 percent in 1977 to 21.4 percent last year.

League economist Thomas J. Parliment said most ratios were in the under-35-percent range, but some ran as high as 40 percent of income spent on housing. Though such loans usually only are permitted when the buyer has no other debts, Parliment called the trend "alarming."

League president Edwin B. Brooks Jr. termed the 40-percent ratio "the absolute outer limit" and pleaded for government action before that limit is reached. Specifically, he called for programs to help first-time buyers, such as special, tax-free savings accounts. The number of first-time purchasers fell from 36 percent of the market in 1977 to just 18 percent two years later. Brooks, noting that there will be 42 million potential first-time buyers during this decade, wondered where the money will come from to fund those purchases if government policies are not changed.

League officials railed against last week's changes in savings certificates rates by federal financial regulators. Rates were permitted to go higher than market rates, and the quarter percent additional interest savings and loans can pay was limited to a narrow range of investments. The decision by the government to allow banks to pay S&L rates when rolling over money market certificates will cost the thrift industry $17 billion in revenues this year, according to Kenneth J. Thygerson, the league's chief economist.