AMID THE CURRENT GRUMBLING that we can't spend the money to repair and modernize our defenses until the Reagan administration can get itself organized and give us a clear agreed-upon strategy , for God's sake, the quiet patient voice of T. Harry Williams murmurs to us -- from Lexington to the 20th century, folks, we've never had a strategy.

Similarly, Williams tells us, our many other military deficiencies, quirks and strengths have long and strangely shaped roots. For example, in this History of American Wars from 1745 to 1918 , completed just before his death, Williams lets the reader see that we have always counted on short wars (it wasn't just a Carter administration idiosyncracy). Occasionally we have been right -- notably, in the case of the Mexican and Spanish-American Wars. But rather often the "our-boys-will-be-home-by-Christmas" folks are tragically wrong: for example, in the Revolution, when Congress asked for only one-year enlistments because it was sure the war would be so short, and in the Civil War, when many on both sides predicted a quick victory.

Further, as Americans -- secure for much of the 19th century behind the protection of the British fleet -- we became accustomed to the luxury of disarming after each conflict. The Jeffersonian Republicans, for example, sold most of the navy after the Revolution and cut the army to 3,200 men. Jefferson's secretary of the treasury. Albert Gallatin, opined that sending all members of the military "to distant garrisons where hardly any inhabitant is to be found" was the best arrangement for that "perhaps necessary evil," but added that he "never want[ed] to see the face of one in our cities and intermixed with out people."

These traits -- neglect of strategy, almost unshakeable belief that wars will be over quickly, enthusiastic and quick postwar disarmament, and peacetime disdain of the military -- are quintessentially American. They are perhaps understandable, given our isolation from the rest of the world until the age of long-range aircraft and missiles, and our peaceful relations (after 1848) with out near neighbors Canada and Mexico. They also doubtless have had roots in our national penchant for pragmatism, for taking problems only as they come, for concentrating on the great adventure of our westward expansion, not foreign foes. Still, this national inability to look, militarily, beyond a very short horizon does not fill one with an overwhelming sense of confidence about how our history has prepared us for our 20th-century role as a world leader.

Through World War I, the period covered by this volume, Williams leaves the impression that things might have been very much worse for us except that we have been very fortunate in our wartime presidential commanders-in-chief.

For great stretches of time during the Revolution Washington carried the nation's future with him. No great strategist at the outset, he learned, led and prevailed.

Polk's shrewd instincts, once the Mexican War began, were to end it quickly because of the threat that public support would fail if the conflict should become stalemated in northern Mexico. In spite of the fact that he distrusted "Old Fuss and Feathers," General Winfield Scott, as a potential Whig presidential candidate (and indeed he had earlier relieved Scott when the general had fulminated in writing to the secretary of war that he feared "fire upon my rear, from Washington"), Polk now turned to his rival to end the war. Scott responded with a brilliant landing at Vera Cruz and march inland, culminating in the conquest of Mexico City -- a campaign remarkable both for its success and for the wisely conciliatory approach Scott showed toward the Mexican population.

An outspoken critic of Polk and anti-war congressman then became our commander-in-chief in our next and worst war. Williams leads one to believe that, from 1775 to 1918, Abraham Lincoln was by all odds our greatest yamerican strategist. An instinctive Clausewitzian without knowing it (Clausewitz had not yet been translated). Lincoln knew that he must defeat Lee's army. His generals, before Grant, were largely disciples of the Swiss strategist Jomini. They were men with lingering affection for some aspects of 18th-century warfare -- taking forever to maneuver their forces and making places, not the destruction of the enemy, their ofjectives. Williams' concise story of Lincoln's travails and persistence, told in depth in his earlier classic, Lincoln and His Generals , is a high point of the book.

Even Woodrow Wilson, as confused about military matters as any president we have ever had in Williams' eyes became a great wartime leader.

The need to be lucky in our choice of presidents -- given our other military failures -- is only one theme. Many other leitmotifs -- that appear to us only as hot issues -- are threaded through our military history. Dissent, for example; citizens of Massachusetts, by voting for McGovern in 1972, showed themselves to be paler copies of their ancestors. In 1847 the Massachusetts legislature declared the Mexican War to be "hateful," "wanton," "unjust," "unconstitutional" and "a war against freedom, against humanity, against justice." In the War of 1812 New England merchants fed two-thirds of the British Army in Canada, and Massachusetts contributed "not a man" in the call for militia.

The brutalization of our own soldiers in Vietnam by the methods used in countering guerrillas was also not new. Many campaigns against Indian tribes, and the long bloody effort to subdue the Moros in the Philippines produces a similiar effect.

Williams describes the intertwining threads of tactics, weapon developments, and battlefield communications so as to illuminate how the wars from the early 19th century through World War I became so bloody: the problem of controlling and communicating with men on the battlefield was so severe, it led commanders to cleave to rigid formations in spite of the terrifying growth in firepower. The result in battle after battle was the wrenching scene of straight, beautifully dressed lines of dead.

It is particularly sad that Williams did not live to complete his survey through World War II, Korea, and Vietnam -- the threads he traces so well took some baroque loops during these wars. It is saddest of allk perhaps, because his voice was an especially clear and civilized one in dealing with this most uncivilized human behavior. Today's threads -- rearmament or retrenchment, volunteers or draftees, the quest for a strategy -- are a good two centuries old in our own history. We could use some patience and historical perspective in sorting them out.

The History of American Wars' only major flaw isn't the author's fault: any publisher who puts out a book of this sort without maps should be drafted and assigned permanently to service under George Armstrong Custer.