Sen. Sam Nunn lost a battle early in July to the Department of the Army. But before this series of engagements is over, the Army is likely to wish it had made love, not war.

Alarmed at declining Army quality, Nunn's idea was to cut the Army by 25,000 while giving Army leaders an incentive to avoid the cut by improving the quality of recruits. For every 1 percent increase in high school graduates, the Army could recoup 1,000 slots. High school graduation, as many Senate debaters pointed out, is no guarantee of soldierly excellence -- but it is a reasonable measure of diligence. High school graduates drop out of the military at about half the rate of non-graduates and, statistically, are much less of a disciplinary problem.

And the Army, so far this year, is only getting about 38 percent graduates -- nearly a third behind its normal recruiting rate for this time of year. Even after all the summer graduates come in and the rate picks up, it will be very hard for the Army to come even close to the share of graduates it used to get, or that the other services and civilian society show: around 75 percent.

By trying to hit the Army on the snout to get its attention, while also striving to be reasonable (and let it avoid all or some part of the cut by improving its percentage of graduates), Nunn probably gave the Army its best argument. The Army said that if its total authorized strength was unknown and unknowable during the year, as the percentage of recruits with diplomas varied, it had a management problem of staggering dimensions.

Why cut the Army at all? To answer this requires some familiarity with a similar situation in the Marine Corps five years ago.

In the spring and early summer of 1975, the Marine Corps was in a mess. Among other things, the quality of its recruits had been allowed to deteriorate sharply. The Senate Armed Services Committee had just cut Marine strength by 4,000 when the new commandant, Lou Wilson, took over. Wilson had a choice to make then. He could have gone to the mat with the committee, and might have won.

But he took a different route. He saw the committee's cut in Marine strength for what it was -- a free offer by someone else to help take the blame for tough decisions you must make yourself. Wilson protested the committee's cuts in a pro forma way; but what he emphasized was that Congress wouldn't let the Marines have their full strength until they solved their problems. He tightened discipline, demanded rigorous training, reorganized recruiting and drove recruiters to go after high-quality people.

The statistics show that he got sharp increases in high school graduates, from 50 percent to 78 percent -- but that's not the best test. Talk to any Marine officer or noncom whose command responsibilities span the last decade about the difference between the Corps in the early '70s and today. They'll say that Lou Wilson made a lot of the right things happen.

One has to be careful in drawing lessons from the Marine Corps and applying them straightforwardly to the much bigger Army. But many of the tough steps that the Army needs to take today are similar to those that faced Lou Wilson five years ago. These are much easier if there is someone else to help take the blame. Nunn and the committee were offering to do for the Army what they had done five years ago for the Marines -- to be the bad guys, to have it said, "Unless we make these changes, the damned Senate Armed Services Committee won't let us have our force structure."

Instead, the Department of the Army mounted a massive lobbying effort. At one point, the threat, from an unnamed source, to close bases in the states of some senators was called "contemptible" by the committee chairman, John Stennis -- probably the strongest word he has spoken on the Senate floor in his 33 years there. And Nunn's ally, All-Volunteer Force supporter Sen. William S. Coben, told of a call to his office threatening attacks on him as being racially motivated against minorities if he supported Nunn. Cohen called this "malicious, pernicious, insidious." A part-time poet, Cohen is clearly committed to understatement.

Such a charge against him and Nunn is also flatout loony, since the Army's enlisted ranks are one major part of American society in which blacks' educational levels surpass whites' -- 65 percent of the blacks who enlisted last year were high school graduates, but only 54 percent of the whites. In the current situation, emphasizing quality means, proportionately, turning away from poorly educated whites.

One battle is over, but the campaign to save the Army has just begun. Before this is all finished, the Army is going to need Nunn and his allies, badly. Friends in Congress are hard to come by.