THE NATIONAL Park System is a conspicuously strange place to pick political fights. But that seems to be the only way that the secretary of the interior, James Watt, knows how to deal with them. It is possible to make a cool and rational defense of the parks budgets under Mr. Watt. Instead he chooses to resort continually to wild exaggeration and accusatory misstatements aimed at his various adversaries, who by this time are numerous.

A sensible defense of the administration's parks policy might point out that the present austerity began in the Carter years. Real spending on the national parks--spending, that is, adjusted for inflation --was cut in half from President Carter's first budget in fiscal 1978 to his last in 1981, drafted when he was desperately trying to eliminate the deficit. Now the Reagan administration and Congress seem to have agreed to stabilize park funds at a level well below that of the early Carter years, but, after three years of drastic budget cuts, that's not bad.

This argument would further point out that the National Park System was greatly expanded in the middle 1970s, for reasons sometimes related to the Bicentennial, and with its limited funds the Interior Department now wants to give priority to maintaining and protecting the present parks instead of adding more land. Not everyone will agree with that precise order of priorities. But the case is a reasonable one and, as we present it here, it has the further advantage of being factually accurate.

It is, if we may say so, a better statement of Mr. Watt's position than you will ever get from Mr. Watt. You can find fragments of it embedded in the various explanations and denunciations that Mr. Watt offers. But there they are mixed in with an intolerable amount of hyperbole and flat error. Why does Mr. Watt gratuitously pick quarrels with Congress by accusing it of cutting park budgets when it demonstrably did not? It's hard to answer that one. Why is he now dragging his feet in disbursing even the modest amounts now being appropriated for land acquisition? Is not the seller entitled to a prompt settlement? But that doesn't seem to be Mr. Watt's style.

He seems to belong to that fraction of humanity that enjoys combat for the sheer sport of the thing. But the result is that he has inadvertently managed to convince the country that support for the parks has been steadily sinking when it has actually risen a little over the past two years.