When Mae West starred on Broadway in her critically panned but crowd-pleasing entertainment ''Catherine Was Great,'' she apologized nightly for omitting many events in the rich and ribald life of the brilliant 18th-century Russian sovereign: ''Catherine was a great empress. She also had 300 lovers. I did the best I could in a couple of hours.''  In fact, according to Simon Sebag Montefiore, the reliable count of Catherine's lovers was more like a baker's dozen. But about which lover occupied the No. 1 spot there is no doubt, as Sebag Montefiore makes abundantly clear in ''Prince of Princes,'' a discursive, meticulously researched and mostly absorbing new biography of Prince Grigory Alexandrovich Potemkin. For nearly 20 years, until his death, Potemkin (1739-91) labored with superhuman gusto as Catherine's ingenious bed partner, sex toy, soulmate, military strategist and commander, party planner, empire builder, naval architect, diplomat, nurse, correspondent, literary adviser, art collector and even pimp, far outlasting other handsome and witty ''favorites'' in the perilous environment at the empress's glamorous yet crude court in St. Petersburg. Catherine (1729-96, reigned 1762-96) and Potemkin may even have been man and wife, although Sebag Montefiore, like others before him, has not found ''conclusive proof'' that they were ever married, as legend would have it.  So formidable did Potemkin's personal and political power become that a memoirist who worked on his staff could reasonably call his boss ''czar in all but name.'' Others coined less flattering labels. The first book about Potemkin, published in Germany in 1794, was called ''Prince of Darkness,'' reflecting the strongly disapproving attitude most Europeans held toward this brilliant, scheming and ruthless statesman -- and even more toward his dissolute, debauched and ''immoral'' private life. (Among other indiscretions, his longstanding sexual involvement with his five comely nieces -- under Catherine's approving eye -- especially grated on less indulgent European sensibilities.) But an admiring Jeremy Bentham, the creator of utilitarianism, who was brought to Russia by Catherine and Potemkin to provide technical expertise in the newly conquered Crimea, overlooked Potemkin's excesses and extolled his friend as ''Prince of Princes.'' The poets Gavril Romanovich Derzhavin and Aleksandr Pushkin devoted many pages to Potemkin's exploits, while Lord Byron developed a near obsession with this larger-than-life ''natural'' personality, who so epitomized the values of Romanticism.  Across the rapidly expanding Russian Empire Potemkin was known simply as ''Serenissimus.'' Serenity is not the trait I would ascribe to this restless, egotistical, voracious, gigantically energetic and boundlessly ambitious character after reading this monumental, densely detailed and at times dizzily panoramic biography. But then, Russians take a different view of serenity -- and of how rulers should behave.  In his introduction, Sebag Montefiore, a British journalist and the author of two novels, points out how Potemkin's reputation has suffered ever since his death, owing to several factors. Most important was his ambiguous status. Although Catherine lavished numerous titles on him (Prince of Taurida, field marshal, commander in chief of the Russian Army), his real position was impossible to categorize. Initially, he was just one of Catherine's sexual ''favorites,'' or mignons. Later their relationship grew into what the French call an ''amitie amoureuse.'' ''Their love affair and political alliance was unequaled in history by Antony and Cleopatra, Louis XVI and Marie Antoinette, Napoleon and Josephine, because it was as remarkable for its achievements as for its romance, as endearing for its humanity as for its power,'' Sebag Montefiore claims.  Arguably Potemkin's greatest achievement was to lead Catherine's armies -- and new Black Sea Fleet -- to victories against the Ottoman Empire along the Black Sea coast and in present-day Romania and Moldova. He solidified these gains by designing and overseeing the construction of many new seaports (like Kherson and Odessa) that established Russia as a power in the Levant for the first time and set the stage for itss grand entrance into the center of European power politics in the Napoleonic era.  After Catherine's death, her son Paul came to the throne. He hated Potemkin even more than he despised his mother, and set about besmirching his reputation. During the 19th century, succeeding Romanov rulers maintained a much more prim and rigid court life than Catherine, and regarded her highly publicized sexual adventures with distaste and embarrassment. After the Russian Revolution, and especially in the puritanical atmosphere of Stalinism, Soviet historians were forced to take an even dimmer ideologically driven view of Catherine and her entourage. So only now is it finally possible, Sebag Montefiore argues, to give Serenissimus ''his rightful place in history.''
Sebag Montefiore has written a life of Potemkin, Catherine the Great's military strategist, literary adviser, party planner and all-around main squeeze.