PRESIDENT REAGAN has vetoed the latest supplemental appropriation bill, inciting speculation that, as headlines say, Fiscal Crisis Looms. High officials warn that the outlook is dark and perilous for much of the federal government -- for example, the Federal Labor Relations Authority -- although, they hastily add, a way will be found to pay the armed forces. The president's veto message was sharply worded, and the congressional Democrats are responding in kind. The general suggestion is one of heavy snorting, stamping and pawing of earth.

Does it not strike you that there is a certain pattern to these collisions? There have been three of them over the past year. The first, last fall, was in the period when the White House was becoming painfully aware of the size of the deficits to be projected in the first Reagan budget later in the winter. You probably recall that, on a Monday morning in late November, Mr. Reagan vetoed the continuing resolution on which the government's spending authority depended. Thousands of civil servants were sent home for a day and the Washington Monument was briefly closed for lack of funds. The episode left a sharp impression of presidential determination to cut spending.

Much the same thing happened in late June, a time when policy was working out badly, with both unemployment and interest rates rising. Congress passed a supplemental appropriation that was, in truth, too big. Mr. Reagan vetoed it. Congress passed a smaller version. Mr. Reagan vetoed that one, too.

Now there has been another veto. The past six weeks have been an uncomfortable period for both Mr. Reagan and his Democratic adversaries. Last month the president reluctantly decided that changed circumstances would require him, despite the shrieks of some of his most vehement supporters, to help pass a tax bill. The Democrats in the House, for similarly good reason, found themselves having to support Mr. Reagan. The current veto of still another supplemental appropriation bill puts everyone back in a more comfortable posture. Mr. Reagan is back in his most congenial role as the scourge of the spendthrift Congress. The House Democrats have returned to their familiar attitude as protectors of the poor and the innocent.

These vetoes, and the posturing over them, are not trivial. They don't make a great deal of difference in the evolving shape of the budget. But they seem to have become an important device for organization -- an opportunity for each team, in a turbulent game, to get back on its own side of the field. It lets everyone return, at least briefly, to the simple and satisfying traditional pieties, after the painful departures that the complexities and confusions of the real world keep requiring.