With this book, planned apparently as the first of a three-tome epic saga about Britain and what the Great War (1914-18) did to its society, John Masters sets out to crown a long writing career. In two ways, it seems a natural choice. The war, which killed three of his uncles and began in the year in which Masters was born, shaped his generation; and, before he turned to writing his early Indian novels and later became a U.S. citizen, Masters was a distinguished soldier in the British Army.

Still one would almost advise the reader to come to "Now, God Be Tahnked" having first let Barbara Tuchman (in "The Proud Towner" or "The Guns of August") paint the general backdrop of Europe in 1914. However, once the dynamic of war gets under way, Masters is in full control and enough the professional to keep some 40 separate characters up in the air without dropping the reader's interest. Those characters in his repertory that don't get the full treatment this time will presumably be given another run in the trilogy's concluding volumes.

Luckily, genealogies are provided at the front of the book as a visual guide to the five family groups - four English and one American - around which the book revolves. Ther e are side plots on poaching and Irish nationalism (unrelated). The central theme, though is the gradual intrusion of the war into people's everyday lives, on the front and at home: Some react with heroism, sung and unsung, and others turn to profiteering and black marketeering. Amid all this, social class barriers begin to crumble.

Conscription, whose introduction is imminent as this book ends at Christmas 1915, was a leveler. The classic noblesse oblige argument against it is put by one Christopher Cate, a sympathetic and sedentary squire, the character who is his Masters' voice in this book. "We owe the country, and the common people something. They give us a standard of living, a way of life, unequalled in history. We owe them, in return, our lives, whenever we are called upon to give them."

But did the Great War really reduce social and economic graduations in Britain permanently? The same was said later of the impact of World War II, yet much of British industry today is seen as deeply riven between bowler-hatted management and cloth-capped workers.

Masters is a caustic observer of the idiocies of army etiquette and the horrors of trench war. Fledgling officers are induced into such mess mysteries as which glasses to drink regimental toasts out of, while, at the front, advances and retreats are bungled, and both Germans and Allies seek the decisive breakthrough by trying to position each other with gas. You really get the feeling here that Masters knows what he's talking about. As he should. At one point during World War II, when he was 30, he was the youngest brigadier in the British Army.

Fed on official propaganda, many British turned violently anti-German or ("Bosch," or "Hun") to the extent of smashing property of Britons with German names and even - if you find this scene in this book credible - hanging dachshunds from lampposts. This and the seamy making of fortunes from selling substandard food at black market prices are well told here.

What jars is Masters' insistence on spattering like shrapnel throughout his book repetitive and generally crude sex scenes. Occasionally, they are apt and do not seem gratuitous. But is it really necessary to have everyone, or almost everyone, indulging themselves with the rapidity of Vickers machine gun fire? Virtually no character escapes. His treatment of homosexuality is, by interesting contrast, of a subtlety that one associates with Masters' earlier works.

Masters' style is different from the classic British novels about World War II - Waugh's "Officers and Gentlemen" triology or Powell's "A Dance to the Music of Time" sequence. Time will tell whether it lasts as well. But this is an excellent beginning.