The conventional wisdom says the honeymoon is over. The conventional wisdom often has a way of looking foolish, but this time it's probably on the mark.

When the August recess began, the administration was basking in the glorious sunshine of its victories on the budget and the tax bills. It proved a rainy month. By this time interest rates were supposed to be dropping. They have remained intractably high. By this time the market was expected to be on an upswing, reflecting confidence in the Reagan leadership. The market has gone to the bow-wows.

In any rational perspective, the fiscal situation -- with one exception -- offers no real cause for alarm. The current fiscal year, ending Sept. 30, will see total federal outlays in the neighborhood of $661 billion. Projected spending for 1982 is $702 billion, a substantial increase. But 1981 outlays are 23 percent of the gross national product, and 1982 outlays will decline to 22 percent. Surely that is a hopeful sign.

Defense spending in the current year is pegged at $160 billion. It will got o $188 billion in fiscal '82. But as a percentage of the GNP, defense spending actually will be significantly less than in the Kennedy-Johnson years before Vietnam. It simply is not true that the butter of social programs has been sacrificed to the guns of defense.

The one worrisome problem that will not go away is rooted in the persistently high levels of federal borrowing. If the '82 deficit could be held to $42.5 billion -- a most unlikely prospect -- the government would be pre-empting about 11 percent of the available capital. When various loan guarantee programs are taken into account, the figure rises to 25 or even 30 percent. The administration's most pressing task is to get this borrowing down -- and it won't be easy.

Fiscal headaches to one side, the president faces otehr worries. As the Senate's hearings on Sandra O'Connor's Supreme Court nomination made evident, the far right wing of his support is fluttering wildly. He will get O'Connor on the high court, but he will pay a price.

Other emotional issues lie ahead. It is hard to see how a divisive fight can be avoided on the question of abortion. Congress has yet to settle a policy on racial-balance busing. Organized labor, already aroused by the president's firmness in the strike of the air traffic controllers, will be battling furiously against repeal or emasculation of the Davis-Bacon Act. We may get into a bitter fight over gun control.

The president won his victories on the budget and the tax bills by putting together a tight bipartisan coalition of fiscal conservatives in both House and Senate. That coalition will dissolve in the rains of autumn and the snows of winter. It will take more than gifts of presidential cuff links to put together a winning season. And problems on the Hill could be fearfully compounded by problems abroad.

Persons who have talked recently with the president have found him in his usual buoyant spirists. He remains cheerfully confident that his economic measures will begin to work in the new fiscal year. He is rested and ready for battle. The trouble is, Congress is rested and ready for battle, too.