CHENNAULT By Jack Samson Doubleday. 365 pp. $19.95 THE MAVERICK WAR Chennault and the Flying Tigers By Duane Schultz St. Martin's. 335 pp. $18.95

THE NATIONAL mood was somber as the United States entered World War II. The U.S. fleet had taken a beating at Pearl Harbor, and Japan was rampant in the Pacific and on the Asian mainland. Germany held sway on the European continent, menaced the British Isles, and was on the offensive in North Africa. The outlook was ominous. Americans badly needed something to cheer about.

They got it. In the skies over Burma and China, three squadrons of American fighter pilots flying shark-nosed P-40s took on hordes of Japanese fighters and bombers in derring-do defiance of overwhelming odds, destroyed them in startling numbers, and were themselves shot down only now and then.

The P-40 pilots had volunteered to fight the Japanese for China as American citizen-airmen before the United States became involved in the war. They had been transformed from ragtag, roisterous mercenaries, many of whom had never flown a fighter, into cool, highly skilled combat pilots. They beat the odds at nearly every turn by virtue of their superior airmanship, gunnery and tactics, which put a premium on fighters attacking in pairs -- a concept that was to become the worldwide standard -- and which downplayed the one-on-one dogfighting that had been in fashion since World War I.

Their leader and teacher was Claire Lee Chennault. He had resigned from the U.S. Army as one of its finest but most frustrated fighter pilots. The Army hierarchy of the time had not yet come to recognize the importance of airpower or of fighters as essential to it, and had given the yawn to the very tactics that the hot pilots of the American Volunteer Group -- the AVG -- had learned from Chennault and were now using so successfully under a foreign flag.

As author Samson writes: "And suddenly -- in the midst of all the dreary news of worldwide defeat -- the spectacular victories of obscure American soldier-of-fortune fighter pilots burst upon the front pages of newspapers and on the newsreels of local movie theaters. Chennault's name became a household word, as did the 'Flying Tigers.' "

The tiger was China's national symbol, and the Chinese, who adulated Chennault and his men, did them the honor of naming them after it. The pilots called their fighters "sharks," however, and flew them accordingly, often so intent on the kill that they risked collisions while raking their adversaries with close-in, can't-miss machine gun fire.

The combat scenes are the right stuff of Samson's sweeping book. In relating them, he relies heavily on the after-action reports of the pilots who had taken part. It is well that he does. They had a remarkable way with words for men of high action, and their accounts have the ring of authenticity amid adventure.

Samson is no slouch as a wordsmith, either. There is little of the poetic about his narrative, but it moves along smartly and does the job. He served with Chennault in China during the war and, after it, in the airline that Chennault was instrumental in establishing there. The author makes the most of this, and of the skills he developed in his subsequent career as a journalist, in telling his story of a complex air warrior who was caught up in some of the most byzantine military and international politics of World War II and its aftermath.

Even after Chennault and his free-lancing flyers had been assimilated in the U.S. military establishment in 1942, its top generals remained leery of him. They resented his having been a renegade from their ranks, took strong exception to his outspokenness, rejected his assessments of what had to be done to defeat the Japanese -- and, later, the Communists -- in China, took their time about sending him the new fighters and other equipment that he demanded, and were at pains to persuade President Roosevelt, who rather respected Chennault and his ideas, that he was usually all wet.

A lot of this had to do with their wariness of -- even distaste for -- Chiang Kai-shek, the Chinese commander-in-chief, whom they suspected of being more concerned with personal aggrandizement than with defeating the Japanese, and whose creature they regarded Chennault as having become. General Joseph "Vinegar Joe" Stilwell, the U.S. commander in the China-Burma-India Theater, called Chiang "the Peanut" and never got along with Chennault. An ingrained infantryman, Stilwell spurned Chennault's advice on the proper use of airpower and his pleas for the permission and the wherewithal to put it into play most effectively.

Samson almost always takes Chennault's side, but by no means blindly. He gives full play to several instances of Chennault's wrongheadedness and to the views of those who opposed him. Chiang Kai-shek is far from a hero in this book. And even though Samson clearly believes that the postwar loss of China to the Communists represented a failure of U.S. foreign policy, he gives that policy and the men who shaped it in Washington their day in court.

After the war, Chennault, by then a confirmed "China hand" if ever there was one, divorced his wife and the mother of his eight children back home in Louisiana, and married Anna Chen, a young Chinese journalist, who in later years would be a major figure in the celebrated "China Lobby" in Washington. Samson tastefully tells about Chennault's relationships with her and with some American women in China. He also describes how the very proper, very smart Madame Chiang came to be the major influence on the Americans fighting in her land.

FOR READERS who would just as soon focus on the Flying Tigers in mainly military perspective, The Maverick War will do quite nicely. Author Schultz, an adjunct professor at the University of South Florida, does an excellent job, in his shorter and faster-paced book, of describing how the AVG was formed and how it fought and fared.

"A legend was born in the skies," Schultz writes of AVG's stunning victories early in the war. His accounts of the Flying Tigers' feats are often superb, and his interpretations of their military significance are succinct and satisfying.

Take, for example, his summation of the AVG's relentless bombing and strafing of Japanese troops massed and trapped at the Salween River gorge: "The victory at the Salween alone would have been sufficient to justify the Flying Tigers' existence. If not for the handful of tired American pilots and their maverick leader, the Japanese would have crossed the river and threatened China . . . Their four days over the Salween may have been their finest."

James W. Canan, a senior editor of Air Force magazine, is the author of "War in Space."