THE AMBASSADORS AND AMERICA'S SOVIET POLICY by David Mayers Oxford University Press, 335 pp., $35 This cool, imaginative, and perceptive study of two centuries of American diplomats in Russia takes a neglected topic and gives it purpose and insight at three overlapping levels: First, as a concise account of Russo-American relations from the American Revolution onward, it demonstrates how constant, minor frictions grew from basic differences between autocracy and democracy - long before communism. Second, it provides a survey of changes in the American diplomatic service since World War I, when a slow-growing professionalism fostered coexistence by moderating those very frictions. And last, it serves as a study of the diplomatic art, its place in the contemporary world, its requirements, potentialities, and limitations. These themes emerge from brisk accounts of the activities of 60-some ministers or ambassadors since 1780. Friction has been normal. First St. Petersburg and then Moscow were true hardship posts, less because of difficult winters and problems with amenities, than because Russian officials feared foreigners, spied on them, read their mail, restricted their travel, and blocked their contacts with ordinary citizens. A Russian posting was something to endure, not enjoy, not least because so few of the Americans knew French, let alone Russian. They could only cluster together, gather political gossip at aristocratic parties, speculate on why the Russians behaved as they did, and count the days before returning home. A new diplomatic generation fared far better. The Rogers Act of 1924 nurtured true professionalism, and the State Department wisely decided on systematic training for a few Russian specialists, who performed remarkably well after diplomatic relations were re-established in 1933. They included Charles (Chip) Bohlen (ambassador, 1953-57), and George Kennan, whose writing on Russia far outshone his intemperate ambassadorship in 1952. Expertise on Russia had at last proved its worth, and other excellent men made similar career choices: most notable Llewellyn (Tommy) Thompson and Jack Matlock, ambassadors during 1957-62 and 1987-91, respectively. These men and others had the confidence born of historical background, an intimate knowledge of Russian and its nuances, and an affection for Russian culture that moved many Russians themselves. Thompson played a vital role as a respected presidential adviser during the 1962 Cuban Missile Crisis, while Matlock rendered yeoman service in interpreting Gorbachev's peaceful revolution. What does this collective experience signify for the diplomatic art? Mayer, who has written about American diplomacy in the early 1950s, and also about Henry Kissinger, tacitly warns us not to expect too much. Reporting local politics, assisting American citizens, making representations, occasionally negotiating, and certainly dispatching advice home - even if rejected: These are the diplomats' tasks. But how is professionalism attainable? Mayer's emphasis is on proficiency, on decades of training and experience. The best, most successful ambassadors were those versed in Russia itself, those with realistic expectations and goals, who understood that hardball was normal, and that personal friendship was irrelevant at the official level. These hard-headed men won Russian respect. Sentiment, no; knowledge and power, yes.