The United States will become a "nation of renters" unless government policies are changed to create more capital for new home buyers, officials of the U.S. League of Savings Associations predicted yesterday.

"The plight of the home buyer in 1981 was a story of capital shortage--not enough savings in the economy to meet the financial needs of home buyers, government and industry," said League Chairman Roy G. Green.

" . . . Without changes in policy, we are going to become a nation of renters," and this would "do violence to the American way of life," Green told a press conference called to release a new study of homeownership.

The report, entitled "Homeownership: The American Dream Adrift," showed far fewer first-time home buyers than at any time in the recent past. A league survey in 1977 showed that 36 percent of all buyers that year were buying their first home. By 1979 that figure dropped to 18 percent, and last year it declined again to 13 1/2 percent.

Other statistics in the survey gave a good idea of why this has occurred. The median price of homes rose from $58,000 in 1979 to $72,000 in 1981, while mortgage interest rates jumped from an average 10.6 percent to 14.47 percent over the same period. This resulted in median monthly housing expenses of $816, a 22 percent increase from the $550 median in 1979. Consequently, to buy an average home, a family had to have $39,196 in income last year, up sharply from the $28,110 needed only two years before.

In addition, Green said, 1981 "may be not an aberration but the beginning of a trend." This is largely a result of a generational shift: In the 1980s, the country will have fewer people in the 45-to-65 age range--when people usually save the most--and more in the prime home-buying group of 25-to-44-year-olds.

"Housing market conditions in 1982 show little prospect for improvment, and the future trends that seem likely to characterize the balance of the 1980s promise a decade of difficulty for home buyers," the study concluded.

The league said that what is needed is more government incentives for saving, particularly more tax breaks, a lower federal budget deficit, less local housing regulations and expanded authorities for savings associations.

While saying these policies are needed to promote homeownership in America, the league continued to oppose the one vehicle that buyers of resold homes used more than any other last year to aid their purchases--assumptions of old mortgages at their older, lower interest rates.

The National Association of Realtors estimated that about 60 percent of all purchases of resold homes last year involved assumptions. But league chairman Green said that the fate of home buyers is tied to the health of the thrift institutions, which traditionally have provided the most mortgage credit. Thrifts have argued that they must have the authority to call in low-yield loans when a home is sold, because they are losing money on these older, fixed-rate mortgages.