The explosive growth of government social welfare programs that has dominated domestic politics for the past quarter-century has come to an end, according to new government figures.

For the first time in more than two decades, spending by all levels of government on social welfare programs has declined as a percentage of the gross national product, the Social Security Administration reports in a new publication.

Mitchell Ginsberg, dean of the Columbia University School of Social Work, called the figures evidence of "the end of an era" of rapid proliferation of these programs, from food stamps to medicare, education outlays to unemployment insurance.

"Very obviously, we've come to the end of the fantastic growth of the middle 1960s and early 1970s," said Rudolph Penner, a director of studies at the American Enterprise Institute.

John Palmer, an economist at the Brookings Institution, said that part of the explanation is that new programs put into place in the 1960s and early 1970s are now meeting a substantial portion of previously unmet needs, thus leaving less room for growth.

As a result, Palmer said, there may be less conflict than expected over tax increases and where to get the money for social-program increases.

"The pressures taxpayers are feeling... may be of less concern than they seem to be right now," Palmer said. With the social programs growing less rapidly, the powerful upward "inexorable pressure" of costs might be less than had been feared.

The Social Security Administration's figures show that social-welfare spending as a percentage of gross national product fell from 20.4 percent in 1976 to 19.7 percent in 1977. In 1965, just before President Johnson launched his Great Society, the figure was 11.7 percent.

Ginsberg, Palmer and Penner aren't ready to say that the percentage will actually keep turning down because it may be a statistical freak caused by a big jump in GNP resulting from the end of the recession.

But all agree that the era of tremendous growth of government social-welfare spending has ended. If there are increases, they probably will be much smaller than they have been in the past.

"The surge is at an end," said Penner. He said he would expect government social-welfare expenditures as a percentage of GNP to move up somewhat as time goes on, because the aging of the population will bring up Social Security, health and other costs associated with an older population. But it won't be at the same rate as in the 1965-75 period.

Palmer said growth could resume and start increasing rapidly if substantial new housing aid or national health insurance programs are passed.

Ginsberg, Palmer and other experts said the leveling off of government social-welfare spending results from factors such as these:

A decline the welfare programs for families with dependent children, resulting in part from a lower birthrate than in earlier decades; in part from a smaller number of children per family (due, Ginsberg said, to availability of abortion); in part from a reduction of unemployment and in part from the fact that most of the families eligible for AFDC are now on the rolls, leaving little room for a terrific upsurge in growth. Added publicity for the program plus a reduction of the stigma in receiving welfare caused rapid growth during the 1965-75 era.

"In the past we used to say that only one-third to one-half of the eligible welfare families were on the rolls.

"Today it's probably 85 to 90 percent," Ginsberg said.

The end of the worst depression since the 1930s, causing reduction in unemployment and welfare, food stamps and other such programs.

The "maturing" of certain social insurance programs like Social Security, whose full scope of coverage was being reached in the past decade. The will continue to grow, but probably not at as rapid a pace as in the past.