Washington — Tension is building in Washington among Republicans over how much time the party has to show that the Reagan economic plan is working.
Mr. Reagan thinks he has time - well into the summer at least - to prove his economic program will lead to recovery. Some Republican strategists argue the turnaround has to occur by June or July if it's to benefit the party in November.
At this point the tugging is between those Republicans who favor a GOP strategy focused on this year's congressional elections and those who emphasize a 1984 presidential strategy. The latter are primarily concerned about vindicating Reagan's fundamental beliefs - at the possible expense of greater GOP congressional losses in 1982.
The President, if he continues to dig in his heels against revision of his economic program, could jeopardize the moderate wing of his party, which he himself defeated in the 1980 GOP presidential primaries.
In fact, in today's Washington battles, his 1980 defeat of the Democrats appears less crucial than his earlier decisive win over GOP moderates.
The Democrats have been largely dealt out of major policy decisions. Every major Democratic alternative in Reagan's first year was defeated. It is the moderate Republicans, led by Sens. Howard Baker Jr., Bob Dole, and Pete Domenici , who are trying to forge by week's end a revised budget that would temper the extremes of the Reagan document. They and their Republican colleagues in the Senate and House are worried that the President's rhetorical barbs against congressional compromisers will leave them in a difficult spot this fall.
The Democrats, except for Sen. Ernest F. Hollings (D) of South Carolina, who has presidential ambitions, are glad they are out of the current political wrestling. ''Why should we risk casualties attacking them (Republicans) when they've got a mutiny on their hands,'' says a strategist for the Democratic congressional leadership. ''Let them fight among themselves. The Republicans won't have an issue to run on this fall. And the Democrats do: unemployment, social security, and peace - and we're on the right side of all three.''
Republican strategists acknowledge that an unbudging, ideological Reagan would leave their clients in a bind.
''The voters may not blame Reagan, but they will blame the local Republican congressman, especially the freshmen, for the state of the economy,'' says Richard Bennett, a New England political consultant with Republican clients.
''Reagan's base is shrinking,'' Mr. Bennett says. ''The group of committed Reagan supporters is getting smaller. Its retreating more to the right.
''The public likes the way Reagan says things, but they disagree with him on issues. There is no match between where Reagan is ideologically and where the majority of voters are.
''It's amazing. On defense spending, the question in '80 was should we increase it, and everybody - Democrats and Republicans - said yes. The question now is, should defense be increased at the sacrifice of social services, and the answer is overwhelmingly no - except among conservatives, who are mostly conservative Republicans.''
''What do you tell a Republican candidate to say?'' Bennett asks rhetorically.
On social and economic issues, President Reagan has failed to widen his base since the 1980 election.
Reagan's ''base'' support is estimated variously from 8 or 10 percent of the electorate to 25 percent, depending on how rigidly the analyst defines ''conservative.'' Reagan picks up support from other parts of the political spectrum for nonideological reasons: They like him personally, or feel it is time to try someone other than the Democrats.
''Reagan's fall has been sharpest among the groups that had been least for him in the first place,'' observes Burns W. Roper, president of the Roper Organization. By the end of his first year, Reagan still had support outside the traditional conservative Republican ranks. Some 26 percent of liberals and 33 percent of Democrats described themselves as Reagan supporters, compared with 82 percent of Republicans who said they were Reagan supporters, and 63 percent of conservatives.
But from earlier Roper readings, the falloff was sharper among liberals, moderates, and Democrats than among Republicans and conservatives.
''Surprisingly, by occupation, Reagan has fallen off most among white-collar, business, and executive groups, and least among blue-collar workers,'' Mr. Roper says. By region, the Reagan falloff in support has been steepest in the Midwest, which earlier had been his strongest region.
Behind all the poring over numbers is a fundamental concern among many Republicans that the White House, or at least the President, is misreading the last election.
''Reagan's mandate was to make the economy work better - to get inflation and interest rates down,'' says Austin Ranney, director of political studies for the American Enterprise Institute, a conservative Washington think tank that has sent several of its members to the Reagan administration. ''It certainly was not . . . a mandate to be conservative even though it ruins the economy.''
Reagan seems as determined to differ from Nixon-Ford Republicans as he does from Democrats. Ideology is more a part of Reagan's appeal than was Nixon's, Mr. Ranney says: ''A lot of Nixon's following was based on his image of experience, competence. Nixon was all over the lot ideologically, from free enterprise to wage-price controls, from anticommunism to rapprochement with the PRC (China).''