President Reagan's commanding edge in Congress in 1981 - the bonanza of 33 Democratic seats won by Republicans in 1980 plus the aid of three dozen Southern Democrats in the House -- will have to be honed again this session, and protected in the fall election, if the Republican is to sustain his momentum.
A study of the new Congress's 1981 voting pattern suggests that on a wide variety of issues, Congress as a whole has not lurched in a new direction. The President has used a narrow margin of support to drive his programs through. First year voting shows that any conservative ideological shift was largely among Republicans, not Democrats.
While the public focus has primarily rested on Reagan's economic wins, a Monitor analysis of findings from an Americans for Democratic Action (ADA) survey of voting on 20 issues -- ranging from defense projects and civil liberties to abortion and budgets -- shows that Congress voted much as usual in 1981.
''There was no real great disruption of voting patterns,'' says Congress expert Thomas E. Mann, executive director of the American Political Science Association. ''Voting patterns are stable over time. There was less high drama, less ideological change, and more traditional politics than generally thought.
''It was really retail politics in the new Congress - trading with fence-sitters. The most important change in the House was the simple replacement of 33 Democrats by Republicans. In close votes, such marginal shifts are crucial.''
Early reports on the new budget, to be released Monday, Feb. 8, pull the President clearly back into the maelstrom of cuts in medicaid, food stamps, housing, and education, while holding defense spending sacrosanct.
His task is made tougher as major banks have again started to ratchet the prime interest rate higher, suggesting financial market worries that federal deficits and a tight Federal Reserve Board monetary policy will force borrowing costs higher, possibly aborting the recovery.
Thus, if Mr. Reagan is to have any chance of getting his new budget cuts and protecting defense, he will have to keep his almost 100 percent backing from House Republicans. If he loses his hold, he will no doubt blame the Democrats. His fall campaign pitch then will be that he needs more Republicans in Congress.
''He's right -- in terms of getting what Reagan wants, there's nothing like having more Republicans,'' observes Mr. Mann.
The ADA ratings showed the House as a whole drifting in a more conservative direction - from a 43.8 percent liberal rating in 1980 to 40 percent last year. However, the Democrats turned slightly more liberal as a group -- to almost 59 percent in 1981 from 57 percent in 1980. And Republicans, reflecting the conservatism of their freshman class, turned more sharply conservative, dropping five points to a 16 percent 1981 average, giving Congress collectively a conservative tilt.
Even in the South, the slightly conservative drift of the new Congress was chiefly a Republican trend, with Republican members moving in a much more conservative direction than Democrats.
Reagan's 48 Democratic allies in the House -- 38 of them Southerners - who sided with him in his pivotal tax vote last August, looked comfortable with their Republicanesque 22 percent 1981 liberal rating. But that is within a point of their 1980 rating -- before Reagan was elected.
Recently, Democratic strategist Peter D. Hart announced that Democrats can now feel free to criticize the President, as the public has grown more skeptical of Reagan's policies.
However, the Democrats' voting in the House and Senate last year showed they have felt free all along to differ with the President.
In three of the four regions of the country, House Democrats voted more liberally than before the supposed 1980 conservative tide swept Washington. In the East and West their liberal ratings averaged 76 percent, 69 percent in the Midwest, and 34 percent in the South. Senate Democrats responded to the Reagan-GOP juggernaut also by voting more liberally -- up seven points in the ADA's ratings to 65 percent nationwide, up 10 percent in the North and up 1 percent in the South.
Congress's voting record by region showed the four US regions continuing to vote more alike, headed in a centrist direction. The gap between the most liberal and conservative regions stayed below 30 points in 1981 as in 1980, compared with a 40-point gap in the 1970s and 1960s.
Far from reflecting a Western, Sunbelt conservative shift, the biggest gaps appear to be within states -- particularly Western states. California Democrats averaged an 81 percent liberal rating on issues, California Republicans 7 percent. Oregon and Washington House delegations showed similar philosophical fault lines.
In the fall, the Republicans could lose 10 to 15 House seats, if the midterm election pattern of recent years holds, and as strategists in both parties think likely. This portends a narrowing of Mr. Reagan's already precarious winning edge.