The first session of the 97th Congress ended yesterday as it began: dominated by President Reagan and his crusade to cut taxes, strengthen the military and reverse a half century of growth in social welfare programs.

The Republican Senate and Democratic House, although split along party lines, came together under the Reagan spell to make more history in a few months than most Congresses have made in two full years.

But the 97th also left a lot to be done next year, and there was some nervousness in both chambers as to the likely economic, social and election-year political consequences of what was set in motion this year, especially if the economy fails to respond as hoped.

Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) summed it up this way: "It is a controversial Congress. Men and women will disagree on the policies adopted by this Congress and this administration, but almost no one, I think, will dispute the proposition that this Congress has made more fundamental changes in the public policy of this nation than any Congress in decades."

The main impact came not in the number or variety of bills that were passed, but rather in two all-encompassing measures that Congress approved before midsummer: a tax cut of nearly $750 billion over the next five years and an almost revolutionary budget that combined huge increases in defense spending with equally huge cuts in social programs.

But the Republicans' cheers over these measures were hardly over before bad news set in. The economy slumped, the projected deficits for the next several years soared, and the president proposed $16 billion in further deficit-reducing steps on top of the $35 billion in spending cuts already approved for fiscal 1982.

Congress balked and approved less than half of the new retrenchments, agreeing even to them only after a testy veto confrontation with Reagan that resulted in a one-day shutdown of most of the federal government last month.

In the process, Reagan had to abandon his campaign pledge of a balanced budget by 1984, and his administration held out the prospect of deficits exceeding $100 billion in each of the next three years unless further spending cuts are made; this caused heavy grumbling even within Republican ranks in Congress. Many Republicans still had not gotten over the shock of having to approve the first $1 trillion debt in history, which Congress did in the fall.

A large part of the problem was that Congress had already made most of the "easy" cuts available in order to reduce the size of the 1982 budget; the next steps seem certain to be harder.

The likely targets: defense spending, taxes and big benefit entitlement programs such as Medicare, Medicaid, government pensions and perhaps even Social Security, although the administration would prefer not to touch that hot potato until at least 1984. Senate Majority Leader Baker and others have complained that non-entitlement or discretionary domestic programs have been cut enough, perhaps too much, and have virtually declared them off limits for next year.

In its preoccupation with the budget, Congress put off action on so-called "social issues" such as abortion, school prayer and busing that could bedevil Reagan's conservative coalition next year. It also failed to complete action on other issues ranging from long-term revision of the Social Security system to clean-air rules and voting rights for minorities, which also must be resolved next year.

Among the surprises of the session was the relative importance of the moderate Republicans, who had been overshadowed at the start by the more exotic New Right conservatives whose stunning 1980 election victories had contributed to the GOP takeover of the Senate for the first time in a quarter century.

It was moderates like Baker and committee chairmen Robert J. Dole (Kan.) of Finance, Mark O. Hatfield (Ore.) of Appropriations and Pete V. Domenici (N.M.) of Budget who set the tone for the Senate, and Northeast-Midwest "Gypsy Moths" who, along with conservative Democrats, held the balance of power in the House. Much of the credit for Reagan's victories in the House also goes to another centrist Republican, Minority Leader Robert H. Michel of Illinois.

Moreover, the New Right conservatives were conspicuously unsuccessful in pushing their agenda of social issues beyond desultory debate on the Senate floor where, in one of the ironies of the year, liberals like Sen. Lowell P. Weicker Jr. (R-Conn.) used the old Southern conservatives' weapon of a filibuster to block new offensives from the right.

Another surprise was the general impotence of the mainstream Democrats, who seemed to adjust less easily to losing power than the Republicans did to gaining it, losing a seemingly endless string of votes to the born-again, Reagan-style "conservative coalition." But the Democrats show signs of rebounding, strengthened by signs of Reagan's vulnerability, along with restiveness in congressional Republican ranks, as the administration heads into its second year.

Regardless of what happens next, however, the institutional rules and procedures of Congress were bent and twisted to such an extent to accommodate Reagan that Congress may be facing permanent changes in the way it operates.

The process of budget "reconciliation," by which committees are instructed to cut ongoing programs, proved an easy way to package and expedite hundreds of individual spending cuts and program changes. And delays in the regular appropriations process, necessitated by continual budget cutting, had the entire government operating on a stop-gap, catch-all "continuing resolution" for several months.

"We've developed legislative crutches that combine everything into one big vote where you're not voting on individual issues but voting either with the president or against him . . . ," observed Rep. Leon E. Panetta (D-Calif.), a widely respected budget expert.

Almost totally overshadowed in the first year were issues of foreign policy. Congress passed a foreign aid bill for the first time in years, and Reagan won approval of his proposed sale of sophisticated radar planes to Saudi Arabia, but most of the focus was on domestic policy, specifically on budget cuts.

There was also relatively little controversy over defense, as Congress swallowed nearly all of Reagan's spending increases, and the anticipated hot fights over his proposals to go ahead with the MX missile system and B1 bomber failed to materialize.

It was in the domestic arena that nearly all the blood was spilled.

Almost every domestic program was slashed and some were killed, although some of the biggest and most controversial of recent pork-barrel projects, such as the Tennessee-Tombigbee waterway and Tennessee's Clinch River breeder reactor, emerged unscathed--thanks to Tennessee's Howard Baker and other friends in high places.

The Labor Department's costly public service jobs program, which once employed as many as 700,000 people, was ended. Unemployment insurance rules were tightened, and trade adjustment assistance for workers who lose jobs because of imports was cut to only a fraction of its former size.

Medicaid payments to the states were cut by about $1 billion, although Congress refused to "cap" the payments as Reagan wanted. Medicare was also cut by about $1 billion, with some of the savings resulting from beneficiaries paying higher charges for services. Public health service hospitals were phased out.

Interest rates were raised for small business loans, postal subsidies were cut and Conrail and Amtrak were slashed back, although not as much as the administration wanted. The Legal Services Corp. survived, for the time being, but its activities will probably be curbed.

Food stamps were cut by $1.7 billion, eliminating more than 1 million people from the rolls. Aid to Families with Dependent Children was cut heavily, especially for working parents, and states were allowed to set up "workfare" programs to require work in exchange for welfare. New subsidized housing units were cut by nearly half and rents for tenants were increased. Funding for school lunches and other child nutrition programs was drastically reduced.

Impact aid to school districts with large numbers of federal employes, such as those in the Washington area, was sharply reduced. Grants to low-income college students were reduced, and a needs test was established for the guaranteed student loan program, meaning less assistance for students from middle-income families.

General health, education and social service programs were cut and some were combined into no-strings or few-strings block grants to the states, but Reagan failed to win the breakthrough for the "new federalism" block grant program that he wanted. Some of the largest programs, such as school aid to disadvantaged children, remained intact if somewhat poorer.

Reagan's biggest budget failure in Congress was its refusal even to consider major cuts in Social Security. After cutting the $122-a-month minimum Social Security benefit, Congress, with Reagan joining in the about-face, changed its mind under a storm of protest and restored the benefit for more than 3 million current recipients and others who will qualify for it by Dec. 31. Reagan proposed other major benefit cuts but withdrew his proposal when it too met with stormy opposition.

Reagan had relatively good luck with appointments, being forced to withdraw his first nominee to head the State Department's human rights program but winning applause for his first Supreme Court nominee, Sandra Day O'Connor, the only woman nominated to the high court in history.

Among the few groups of people who came out ahead financially in Congress this year were federal workers, especially high-level ones whose pay cap was lifted, and members of Congress themselves. For federal workers as a whole, there was a 4.8 per cent pay increase, with more approved later for executives and other higher-level officials. Congress treated itself to more generous tax deductions and an easing of restrictions on taking money for speeches and other outside activities.

Another winner was the consortium trying to win waivers to finance the Alaska natural gas pipeline, which consumer groups, rallying too late to stop the drive, protested would be financed by consumers regardless of whether they receive any gas from the line.

Environmentalists won some rounds, as Congress blocked leasing of some wilderness areas for oil and gas exploitation and prevented diversion of park land acquisition money.

Pressure to rewrite and relax the Clean Air Act ran into Senate opposition, resulting in deferral of the act's extension until next year.

Telecommunications deregulation was approved by the Senate and awaits action in the House.

Also put off was the proposed expulsion from the Senate of Sen. Harrison A. Williams Jr. (D-N.J.) for his involvement in the so-called Abscam scandal. Other members of Congress involved in Abscam have left the House by way of defeat, resignation or expulsion.