Of all the questions overhanging politics in this summer of 1981, the most intriguing -- and the one with most long-term importance -- is the possibility that we are witnessing a major realignment that will make the Republican Party the new majority party in America and consign the Democrats to a minority of quarreling factions.

Part of the fascination is that the answer is unknown. Everyone agrees that it will take at least one more election and perhaps two before we can judge the permanence of the current Republican surge. The debate will be open at least until November 1982 and perhaps for two years more.

But in the past week, two careful students of these affairs -- Republican pollster Richard Wirthlin and Democratic consultant Horace W. Busby -- have offered fresh evidence and judgment supporting the realignment theory.

Wirthlin, who polled for Reagan in the 1980 campaign and does monthly surveys now for the Republican National Committee, has been very cautious about embracing the realignment view. But in an interview in which he made public the details of his most reent data, Wirthlin said that while "political attitudes are still volatile . . . if the president's party delivers, we can expect a lot of these former Democrats and Independents to stay with the Republican Party a long time."

At the same time, Busby, a White House aide to Lyndon B. Johnson, informed his business client that the splits now showing between Sun Belt and Industrial/Labor state Democrats in Congress have the potential for dynamiting the Democratic Party in 1984. As he put it, "The Democratic Party cannot make it through the presidential election year without facing its internal liberal-conservative division."

Busby raised what has to be a nightmare possibility for the Democrats: a split so severs that it might produce rival Democratic conventional in 1984.

The Sun Belt conservatives [among congressional Democrats] by and large do not believe the GOP candidates can defeat them, but they can be defeated by their own party's posture and performance nationally," he said. "Hence, if in 1984 the Democratic platform and ticket affront the party's conservatives, the stage would be set for a second Democratic convention to field an alternative national ticket. Following past precedents, such a Conservative Democratic Party might nominate -- who else? -- Mr. Reagan."

That will sound farfetched. But Wirthlin's figures -- of which Busby was unaware when he wrote -- at least take it out of the realm of fantasy. Wirthlin, along with other private and public opinion-takers, has been picking up a significant surge in the number of voters who identify themselves as Republicans. If you count the leaners in his mid-May poll, the Republicans had virtually erases their historic disadvantage and drawn even with the Democrats.

An NBC-AP poll taken at the same time had almost identical results. Other polls -- including those of the Gallup organization, CBS-New York Times and ABC-Washington Post -- still find the Democrats in front. But what is interesting is the source of those Republican gains that everyone finds are coming.

They are coming among men more than women; from union families more than non-union; from middle-income groups ($15,000 to $40,000) more than those at either extreme of the income scale; from high school and college graduates more than those at the bottom or very top (graduate degrees) of the education ladder. They are coming, in short, in what has to be the heart of any majority party coalition these days.

The age picture is very interesting. According to Wirthlin, the biggest Republican gains are coming among young people in that baby-boom generation under 35; the gains scale downward as the age curve ascends. But if you look at the Democratic side of the picture, you see a reverse image: the heaviest losses are among the older voters, the lightest among the young.

The explanation, Wirthlin thinks, is that those older voters cast their first ballots in the Depressing; Democratic Party loyalties keep them from going all the way to the GOP in one jump; so their move has been into the Independent column, while younger voters, who started as Independents, are moving to the GOP.

Thus, the picture that emerges is of a rolling realignment -- a glacier that is up-rooting the lightly attached younger voters more easily than it is the older voters with their deeper Democratic roots. But the glacier is moving in the Republican direction. Of all the sub-groups Wirthlin examined, only one was more Democratic in its identification in May 1981 than in June 1980: the blacks.

These findings and Busby's somewhat parallel observations are more speculative than definitive at this point. But the speculation is enough to suggest that this may be an era of historic political change.