ON TELEVISION last week, Sen. Daniel Moynihan was deploring the effect the new Gramm-Rudman budget process might have on defense. Sen. Phil Gramm, a guest on the same program, feigned astonishment that "one of the weakest" supporters of defense "in the country" had suddenly been moved to speak on the military's behalf. The Gramm remark was crude and wrong, and Mr. Moynihan, an old hand at the art of indignation, quickly shot it down. Case closed -- but it was the wrong way to start this year's defense debate.

It is pretty well agreed that the large and largely necessary budget increases of the first Reagan term are over for defense. The question is what will replace them -- what will now be policy for the long haul. The issue arises in a year when control of the Senate and the deficit are both at stake -- not a propitious time. The defense debate should not become a matter of cheap shots.

What is the right path for defense? It is easier to say what is not. A national decision was made, beginning in the Carter administration and greatly strengthened in Ronald Reagan's, to modernize the military and reverse the post-Vietnam decline. Military strength had been allowed to fall too far behind. There have been debates of many kinds about the buildup that ensued, but the basic decision was necessary and right. The deficit to which it contributed is not the occasion to undo it. The defense budget should not be regarded as an answer to the deficit problem, as a kind of inverted purse.

If the first round of Gramm-Rudman spending cuts takes effect as scheduled March 1, the Pentagon will end up with several billion dollars less in spending authority this fiscal year than last. Outlays will still rise on the strength of past appropriations, but the tap will have been turned down for the future, the more so if you take inflation into account. Continue to turn it down and in time you vitiate the buildup. A tax increase, not a squandering of the last five years' defense gains, is the way to close the deficit.

Actually, the president will seek to extend the buildup. He has indicated that, in the budget he is scheduled to send Congress next week, he will request an increase in spending authority for defense of 3 percent beyond inflation. That is also the long-term growth rate he has now adopted. It is lower than the rate he once envisioned, but higher than it sounds. Spending authority would rise by more than $20 billion a year, from less than $300 billion now to close to $400 billion by 1990.

If spending authority were to rise by only the inflation rate each year, these increases would be cut roughly in half. Congress should take this rate of rise -- the year before, plus inflation -- as a rough guide in defense, just as it does for civilian programs. From there the narrower questions concerning weapons programs can be addressed. The deficit should serve as a discipline to focus those program decisions. Restraint can be a good influence in defense as well as in fiscal policy.