In the 95the Congress, the concerns of the middle class and America business clearly displaced the agenda of social and economic issues that has dominated congressional politics since the inauguration of the New Deal 45 years ago.

This overwhelmingly Democratic Congress chose to raise Social Security taxes while cutting the tax on capital gains. It rejected virtually every proposal put forward by organized labor; on many issues, it gave ground to business. It gave the oil companies a natural gas price deregulation bill they had sought unsuccessfully for 25 years. It willingly voted large increases in defense spending but shied away from expensive domestic initiatives and concentrated on cutting the federal budget deficit.

By the end of this Congress' two-year lifespan, majorities in both House and Senate were searching feverishly for legislative acts that could cater to a "tax revolt" that many members believed was sweeping the country.

That political calculation was symptomatic of the 95th. It was based on the belief that middle-class Americans - home-owning, employed and relatively prosperous - would no longer vote for politicians whose principal concern appeared to be the have-nots rather than the haves.

The 95th was "caught between eras," in the words of three-decade Rep. Richard Bolling (D-Mo.), "uncertain as to what to do and uncomfortable in its uncertainty." The result was an active but uninnovative Congress, which had no stomach for new government undertakings but also lacked the confidence to abandon old ones.

Part of the uncertainty Bolling described was the product of an uneasy relationship with a new president filled with enthusiasm for a long string of campaign promises but ignorant of the rites of Congress and initially unwilling either to stroke or intimidate congressional egos.

In 1977, President Carter demanded that Congress respond to an unprecedented volume of new initiatives, and Congress initially balked. But over two years Carter and his aides learned a great deal about both the volume of work Congress could perform and the methods he could use to persuade the membership to do that work.

Symbolic of Carter's growing mastery of congressional politics were his victories on foreign policy issues, beginning with the dramatic two-vote triumph on the Panama Canal treaties, followed this year by successes on arms sales to the Mideast, the lifting of the Turkish arms embargo, and finally the foreign aid bill.

Carter had more trouble enacting a domestic program. His boldest proposals, regarding energy, were seriously weakened. But the Congress did overcome a historic inability to act on energy, and by the end of the session the White House could express satisfaction with Congress' accomplishments in this and several other fields.

Among these were civil service reform, airline deregulation, a new approach to federally financed water projects, and ratification of executive branch decisions to drop two expensive weapons systems, the Air Force B1 bomber and a nuclear-powered supercarrier for the Navy.

However, any assessment of Carter's success must depend on the standard used. Measured against the long list of legislation the president requested, he got less than half. Measured against what can realistically be expected from the personalities and procedures that reduce the congressional output to a snail's pace, Carter did quite well.

With his campaign promises and the desires of traditional elements of the Democratic Party coalition pressing on one side and his perception of political realities on the other, Carter eventually sacrificed many of the promises, and disappointed much of his liberal constituency. He did not press for welfare reform, tax reform, his urban program or national health insurance. In health, education and welfare the 95th Congress accomplished very little.

Despite a last-minute success in the Senate, Carter failed to win approval for his one serious health initiative, compulsory hospital-cost containment. He lost on election reform, labor law reform and an agency for consumer protection.

In the obsence of any consensus on national interests, special interests reigned - or at least those special interests that reflected the conservative mood.

Labor, with perhaps the greatest expectations about the heavily Democratic Congress it helped elect, lost the most. Apart from an increase in the minimum wage and a badly debilitated Humphrey-Hawkins employment bill, labor had nothing to show for its efforts. Labor law reform, intended to facilitate union organization, particularly in the new industrial South, was defeated. So were bills to liberalize the rules governing picketing at construction sites, to help maritime unions, and to permit government workers to participate in partisan politics.

Business, on the other hand, did quite well, first in defeating the labor movement's initiative, then in winning new investment incentives in the tax code and the capital gains tax reduction. The business lobby helped block creation of the agency for consumer protection, and its distress over government regulations helped win - among other things - postponement of new auto emission standards in the Clean Air Law.

The medical profession and hospital industry proved stronger than the president by blocking his bill that would have controlled the rapidly escalating cost of hospital care.

The right-to-life lobby again prevailed in curtailing government-funded abortions.

Exceptions to this general trend were rare. One was the surprising victory by the women's movement, which pushed through Congress an extension of the deadline for states to ratify the Equal Rights Amendment.

Civil rights groups made a test case of the constitutional amendment that would give the District of Columbia voting members in House and Senate and it won in both houses.

Environmentalists were generally pleased with a strip mining law, a vast expansion of national parks, and the presidentially imposed elimination of numerous water projects. They failed to push through a bill that would have put about 100 million acres in Alaska into federal parkland.

"Respresentative government on Capitol Hill is in the worst shape I have seen in my 16 years in the Senate," Edward M. Kennedy (D-Mass.) said yesterday. "The heart of the problem is that the Senate and the House are awash in a sea of special interest lobbying and special interest campaign contributions . . . We're elected to represent all the people of our states or districts, not just those rich or powerful enough to have lobbyists holding megaphones constantly at our ears."

Kennedy, of course, is one of the few members of Congress who will still voluntarily call himself a liberal. Many other members think the new mood in the Congress is just right. "A most progressive Congress," the Senate majority leader, Robert C. Byrd (D-W.Va.), said yesterday.

Some congressional behavior this year was simply baffling - perhaps a consequence of the political uncertainty prevailing on Capitol Hill. For example, a nervous House and Senate chose to impose whopping increases in the Social Security's tax (they take effect next year) rather than cushion the taxpayers' pain by tapping general tax revenues to replenish the Social Security trust found. The political consequences of that act will be felt in the second half of next year, when most Americans' paychecks no longer fatten as they traditionally have when their Social Security contribution was paid up. In 1979 it will take all year for most people to pay it up.

The nature of this Congress was exposed recently when the Senate had a chance to vote on a proposal that would have eliminated tax deductions for first-class air travel by businessmen (coach seats would have remained deductible), business meals costing more than $25, and corporate purchases of tickets to sporting events for clients "entertainment." Here were loopholes that benefit a tiny fraction of the population, but the Senate rushed to retain them all by a 70-to-22 vote.

Half the 70 votes to retain those loopholes were cast by Democrats - a good indication of the ideological muddle inside the majority party these days.

The changing nature of the Democratic Party is even more obvious in the House, where half the 287 Democrats have been elected to Congress since 1972.

Many of the newer Democratic members were elected from Republican or marginal districts. Their constituents consist more of suburbanites than either farmers or city dwellers, and many are affluent independents without party loyalties.

With voters like these at home, members take on middle-class issues, not social crusades. And the members themselves seems as ill suited to traditional liberal-conservative labeling as President Carter himself.