Slowly, and with all the caution befitting their self-image as scientists, those who teach and study American politics are beginning to say that President Reagan has ushered in a major change, and perhaps a new era, in the government and politics of this nation.

Their term for the changes is "realignment." And in the last four years, it has moved from being a whispered word among a minority of political scientists to open debate and now to a case of growing consensus.

Most of the major papers on realignment presented at the annual meeting of the American Political Science Association here found strong elements of fundamental change at work in the 1980 and 1984 elections, suggesting some but not all of the patterns of the Franklin D. Roosevelt elections of 1932 and 1936. FDR's New Deal coalition stayed in power for 20 years and persists in part even today, many scholars think.

Republican gains in voter identification, Reagan's support among young and first-time voters, the emergence of the South and Mountain West as Republican rather than Democratic bastions and the persistent support for many conservative policies all suggest a shift that may last beyond Reagan's time, the pro-realignment analysts contend.

They hedge their judgment with many qualifiers, and their views are rejected by a minority of skeptics. But within the profession, the tide has clearly changed from 1981, when James Stimson of Florida State University expressed the prevailing sentiment at the annual meeting in saying, "I'm struck by the lack of evidence of the realignment everyone talks about on the news. There just seems to be nothing out there."

This year, more people found something out there, and more than a dozen papers explored the evidence in the National Election Studies of the University of Michigan and various newspaper polls.

The skeptics were people like Walter Dean Burnham of the Massachusetts Institute of Technology and Martin P. Wattenberg of the University of California at Irvine, who essentially argued that voters' party loyalties have become so weak, in an era of personality and television politics, that the reported Republican gains may not mean much.

Burnham said, "The only way, in my view, that a stable Republican ascendancy . . . could be sustained even in the intermediate run would be if the policy counterrevolution of 1981 and later was associated with our climbing back toward the world hegemony, especially economic hegemony, which we once took as a matter of course . . . . The evidence on this front is, however, all the other way."

Wattenberg termed it "the hollow realignment," arguing that "even if the Republican surge is a long-lasting one, it will be of limited importance as long as partisanship in the electorate continues to decline."

But many other scholars are more impressed by the shifts they see in key voting blocs, which they say add up to a pattern of politics fundamentally different from the New Deal era.

Three University of Rochester writers, Harold W. Stanley, William T. Bianco and Richard G. Niemi, cited evidence that such shifts have been under way since the 1964-68 period, linking them to the race issue and the inroads the Republicans made in Dixie through the "southern strategy." But they cautioned that "if the New Deal coalition is not alive and well, at least its corpse has yet to disappear."

Herbert F. Weisberg of Ohio State University said it would take one more election, with someone other than Reagan at the top of the GOP ticket, to be sure. But he said he was struck by the "increased polarization between the parties" and their support groups in the electorate.

Helmut Norpoth of the State University of New York at Stony Brook agreed, arguing that GOP support among younger voters represents "the new generation gap in party identification that sets the stage for a party realignment . . . ."

Two of the most prestigious election analysts, J. Merrill Shanks of the University of California at Berkeley and Warren E. Miller of Arizona State University, acknowledged in a lengthy paper that they found far more evidence of realignment in 1984 than four years earlier.

As they put it, "The directional changes in partisanship that took place between 1980 and 1984 were much more dramatic, for they suggest that a long-awaited party realignment may have begun."

Noting a massive shift of conservative Democrats into the GOP and arguing it was not just among young people that Reagan scored gains, they said, "However hazardous it may be to predict the future, we are persuaded that the 1984 election produced substantial and potentially crucial changes in the distribution of party identification within the American electorate."

Shanks and Miller were cautious over whether there was a clear trend to conservatism, noting that most voters seemed to be expressing satisfaction with the status quo after four years of Reagan's presidency and that the minority who wanted a change of policy hoped for a move in the liberal direction.

But Richard W. Boyd of Wesleyan University said his analysis indicated that "policy as well as performance judgments underlay both of the Reagan victories."

In a focused analysis of Texas, James A. Dyer, Arnold Vedlitz and Stephen N. White of Texas A&M and David B. Hill, a private pollster, said surveys through July show clear evidence that Republicans have attained near-parity with Democrats and that "Texas is becoming a two-party state."

The GOP gains, they said, are fed by migration, conservative Democrats' disaffection with the increasing liberalism of the national and state party and allegiance from young voters. If the GOP can cement the last group in 1986 and 1988, they argued, "a long-term change may be in the making."

The boldest prediction came from Martin Shefter and Benjamin Ginsberg of Cornell University, who examined changes in government policies and parties and said Reagan has built the base for long-term Republican gains.

"Uncertain as they may be," they concluded, "the prospects for an enduring realignment in American politics are stronger today than they have been for at least a generation."