Americans are well on their way to having a federal government whose main tasks are to "defend the shores, deliver the mail and write retirement checks." And little else.

That conclusion arises from the annual report of the Congressional Joint Economic Committee, released yesterday, which documents the Reagan administration's striking success in cutting back on a broad range of activities by the federal government.

The JEC analysis divides the budget into five categories: defense and foreign affairs, aid for the elderly and disabled, net interest on the debt, assistance for the non-elderly poor, and the final category, "everything else."

"Everything else" includes the day-to-day expenses of running the government and an array of programs from education and cancer research to highway construction. This category is the main casualty of the administration's campaign to cut federal spending.

In percentage terms, the only categories of federal spending that have grown since 1980 are defense and foreign affairs and interest payments on federal debt.

Defense and foreign affairs rose from 25 percent of federal spending in 1980 to 28.5 percent in 1985. Net interest on the debt rose from 9.1 percent to 13.8 percent. Programs for the elderly and disabled declined slightly from 37.6 percent to 36.7 percent. Support for the non-elderly poor declined from 7 percent to about 6.3 percent.

The "everything else" category of the budget has already absorbed a $25.8 billion reduction from 1980 levels, figured in 1980 prices, the JEC said. It would be reduced by an additional $34 billion in real outlays under the president's FY 1986 budget, the JEC said. (Its report preceded the Republican deficit reduction plan now on the table.)

"That would mean that the 'everything else' portion of the budget would have been slashed from 21 percent of federal outlays in 1980 to about 11 percent in 1986," the JEC report concluded.

Liberal Democrats, like Rep. David Obey (D-Wis.), chairman of the Joint Economic Committee, call these programs social "investments."

"The category is made up of everything government invests to train people, to educate people, to wage war against disease -- everything that the government does to clean up the water and air; everything that government does to build and maintain waterways, airports, and highways," the JEC's Democrats said.

Lost investment opportunities today mean lost returns in the future, the Democrats contend. "Reduced spending on highway and sewage treatment construction, energy research, job training, strategic petroleum reserves, education, health research or soil conservation will ultimately have their major impact on society years, and even decades, after the cuts are made."

Conservatives argue that these are activities better done by the private sector or by government closer to the people. Education can best be handled at state or local levels. The rebuilding of highways and bridges is a city, state or regional responsibility.

But a strong argument can be made that local and regional solutions can't deal adequately or fairly with the fallout from the severe pressures on the economy since 1980.

The impact of an overvalued dollar is hammering the manufacturing sector, as the unemployment data and the most recent corporate profit reports testify. A Bureau of Labor Statistics survey in January 1984 identified over 5.1 million workers who lost long-term jobs during the previous five years, usually because of plant closings, the JEC report said.

Forty percent -- or two million of these workers -- had not found new jobs at the time of the survey.

Forty percent of these displaced workers live in eight states whose economies are dominated by heavy industry -- New York, New Jersey, Pennsylvania, Michigan, Ohio, Illinois, Indiana and Wisconsin, the report noted.

In addition to sharp regional disparities, there are great differences along lines of race and age in the toll of unemployment on society. Nearly 60 percent of those over 55 have failed to find other jobs. Unemployment rates are also much higher for blacks and Hispanic displaced workers than for whites, the JEC notes.

There isn't a real debate going, of course, about the federal government's proper role in dealing with such problems. The tax cuts of 1981 that created the deficit crises that lie ahead have forced all sides in Congress to focus just on the spending reductions.

One conservative who would not quarrel with the results, has worried about the method. Economist Herbert Stein, writing in his book "Presidential Economics," says:

"Perhaps it is not possible to create rules of policy by discussion and conscious agreement. If so, we are destined to be governed by accident and by the shifting balance of political power among competing interests."

In Stein's view, liberal politics had carried federal spending much too far in the wrong direction. "But Reaganism was more a shriek of horror than a program for solving real problems. It did not make use of the opportunity to find better solutions, but the opportunity and the need remain."