No one has written with more intensity, clarity and compassion about World War I than Pat Barker. Her Booker Prize-winning "Regeneration Trilogy" dealt mainly with the aftershocks of war as men came home wounded in body and mind. At the center is a real historical figure, Dr. William Rivers, who first identified "shell shock" -- what we have come to know only too well as the blandly named post-traumatic stress disorder.

In her new novel, Barker returns to that first apocalyptic conflict, which decimated an entire generation of young men. (In the British empire alone, about 703,000 were killed and 1.5 million wounded.)

The first half of "Life Class" follows the lives and loves of four young people who become entangled in interlocking love triangles. It's the late summer of 1914, and London is going about its business, though uneasily listening to rumors of war. Paul and Elinor are students at the Slade School of Art, where they are taking life-drawing classes from Prof. Tonks, a surgeon turned teacher who, like Rivers, is taken from real life.

Paul has an affair with Teresa, an artist's model, but really loves Elinor. Kit Neville, a former student who already has made a name for himself, is hopelessly in love with Elinor, who loves herself and is in no hurry to lose her virginity. Paul, who unlike Kit and Elinor comes from a working-class background (his grandmother was a slum lord), has a chip on his shoulder and doubts his talent as a painter. On a sultry night in August while on a walk with Elinor, Paul works up the courage to kiss her and is as surprised as she is that she reciprocates.

By September, ambition, rivalry and love are swept aside by conscription and the business of going to war. The leisurely pace of the novel shifts into high gear.

Kit becomes an ambulance driver near Ypres, Belgium, and Paul is sent there, too, as a hospital orderly. The "hospital" consists of a group of sheds staffed by a head nurse, one surgeon and a few orderlies. Within a month, Paul has already seen every possible wound and mutilation, and has bandaged up men with missing limbs or gangrene or whose faces or stomachs are half blown away.

Barker makes us see, smell and hear the horrors Paul copes with. By the time Elinor arrives for a visit, she finds a harder, more impatient man. He has had to "leave ... compassion at the door" to go on with his bloody job. Despite passionate love-making, they have grown apart. Elinor wants to shut her eyes to the war and live in her art. Paul tells her he's drawing the terrible reality around him and muses bitterly that no gallery would show the real face of war. Elinor imagines people "peering at other people's suffering and saying, 'Oh my dear, how perfectly dreadful,' and then moving on to the next picture. It would just be a freak show."

The novel can be seen in two halves: The first celebrates the beauty of the human body that war mangles and desecrates. It's not as compelling as the second half, in which we experience Paul's terrible coming of age. It's as good as anything Barker has written. But even here, immediacy and tension are broken by passages given over to a correspondence between Paul and Elinor.

The book ends on an irresolute note. The war is still young, after all, and anything could happen; no one's fate is yet decided. I think I spy a sequel on the horizon, and if there is one, I hope it will star Prof. Tonks, who returned to medicine on the battlefield. In the pioneering techniques of plastic surgery, he took on the job of drawing mutilated men before, during and after surgery. In addition, Barker says in her acknowledgements, "he embarked on a series of sixty-nine portraits of facially mutilated men which are among the most moving images to have come out of any war." They were not shown until many years after the war had ended.

Brigitte Frase of Minneapolis also reviews books for the Los Angeles Times.