The defense debate is at a turning point, and the participants are regrouping. There is still a fight in Congress over the military program for the fiscal year just begun. The legislative question is whether to give the Pentagon a $10 billion increase in spending authority to cover inflation or, as a sizable group of House Democrats would prefer, hold its budget to last year's level.

But the broader issue of which this is only an example is the defense spending pattern for the future. If the big budget leaps of the first four Reagan years are over, what replaces them? The administration has taken as its new standard the steady after-inflation growth rate of 3 percent per year envisioned in the current congressional budget resolution. But that is a larger amount than it sounds -- it would let defense spending authority rise an estimated $95 billion, or 31 percent, by 1990 -- and it is unclear that Congress will vote that much. So there is a lot of jockeying for position.

House Armed Services Committee Chairman Les Aspin, who conducts a kind of shuttle diplomacy between the wings of his party on the defense issue, is holding a special set of hearings on the buildup to date and where to head next. He put out a faintly revisionist report this week suggesting that the "immense budgetary increases" of the Reagan years have produced only "minuscule improvements" in most areas of measurable strength; he cited rising per-unit weapons costs as one ominous reason.

In the Senate, Armed Services Committee Chairman Barry Goldwater and ranking Democrat Sam Nunn have set in motion a parallel examination of the process by which defense decisions are made. Their complaint, which Mr. Aspin also makes, is that Congress and the Defense Department are so preoccupied with current budgets and short-term considerations that they never reach long-term and strategic questions. Mr. Nunn wryly pointed out in recent speeches that Congress last year "changed the number of smoke grenade launchers and muzzle bore sights the Army requested . . . directed the Navy to pare back its request for parachute flares, practice bombs and passenger vehicles . . . specified that the Air Force should cut its request for garbage trucks, street cleaners and scoop loaders," while glossing over various major new weapons starts that could add as much as $200 billion to future budgets.

The administration has also been busy on its side. Deputy Defense Secretary William H. Taft IV carefully spelled out in one recent speech the wished-for weapons that the services will have to forgo just to get within the 3 percent growth path -- "20 percent fewer Bradley fighting vehicles . . . almost 30 percent fewer Patriot air defense missiles . . six Aegis ships . . . a 20 percent reduction in tactical aircraft for the Air Force and a 15 percent reduction for the Navy. . . . The list of critical weapons systems lost goes on and on." Defense Secretary Caspar Weinberger this week devoted an entire speech to the subject, "What Is Our Defense Strategy," partly in response to those who say the buildup has been formless and has lacked clear goals.

You can expect a lot more talk of this kind in the next several months as the parties feel their way into the future. It is weighty stuff, but a healthy trend. In a sense the defense debate is only now getting serious.