It took Franklin D. Roosevelt, the Hudson Valley patrician, to come up with the New Deal. It took Richard Nixon, the mud-slinging anti-communist, to establish relations with what he used to call Red China. And it might -- just might -- take Ronald Reagan, a Republican raised on the homilies of General Electric, to give us the sort of tax code that could, to revive an epithet thrown at FDR, make him a traitor to his class.

Reagan, we are told, understands this full well. Having looked at the model tax code drafted by that most unlikely of all reformers, Treasury Secretary Donald Regan, the president reportedly noticed that it would abolish deductions for country club membership fees and allowed as how his friends wouldn't like that. That's the understatement of the year. Should Regan's tax plan manage to win the presidential seal of approval, Reagan will have no friends.

But boy will he have admirers! They will include writers on both the right and the left, not to mention, possibly, historians of the future, who will say that Reagan saw his opportunity and seized it. With one bill, he transformed the GOP from the party of the country club, of Big Steel and Big Auto and of all things big and powerful (except, of course, labor) into the party of the vast middle class -- the party that the Democrats used to be.

Of course, the president has not yet said he will do any of these things and, anyway, he is not anywhere near the pioneer in tax reform that he may ultimately appear. Others in both parties have led the way. But the fact remains that should Reagan get behind a tax simplification bill, it will become both his bill and his initiative. He will get both the credit and the blame, and history, not to mention the voters, will hardly remember Kemp or Kasten, Gephardt or Bradley.

No one recognizes this better than Democrats, some of whom realize that their party will continue to pay the price of its nomination of Walter Mondale in 1984. By an irony too rich even for columnists to digest, the candidate who talked almost incessantly about fairness and equity somehow managed to let the Republicans and their president emerge as the potential instruments of tax reform. If only because Gary Hart was right -- if only because Mondale did represent the past -- a presidential campaign was waged by a Democrat in such a way that the GOP is positioned to become the progressive party.

To some Republicans, especially the party's young congressmen, this is no surprise. They talk of themselves and their movement in almost Marxist terms, only their historical determinism is not rooted in class but in generational politics and the inventiveness of their ideas. The split over tax reform will not be partisan, they say, but generational. Younger members of both parties will be for it, and older and more established members against it. Even so, they say, the Republicans will get the credit. The GOP is in the ascendancy, and all the Democrats can do is what the GOP had to do the previous 50 years -- buy in.

In the meantime, though, we all have to wait on Ronald Reagan. Will he join his party's Young Turks and give his country club pals heartburn? Or will he, as the Democrats hope, leave tax reform for younger men and another administration? For help in making up his mind, he ought to look to the man he most admires, Roosevelt, and think of what he would have done. You don't get called a traitor to your class for nothing.