LIES OF SILENCE By Brian Moore Doubleday. 197 pp. $18.95

AT THE START of Brian Moore's 15th novel, Lies of Silence, Michael Dillon is an ordinary man with a sticky, but ordinary problem. A failed poet turned successful hotel manager, he intends to leave his wife, the beautiful but petulant Moira, in favor of his lover Andrea, a radio journalist 12 years his junior. He arrives home from work to find Moira in a combative mood, however, and loses his nerve, deciding to tell her in the morning.

By the end of the first chapter, Dillon and his problem may seem ordinary even to the point of dullness, but in this novel context is everything: the setting is present-day Belfast, and Dillon's marital difficulties are simultaneously overshadowed and enormously complicated by the intrusion into his house in the middle of the night of four armed, masked youths, members of the Irish Republican Army. In the morning Dillon finds himself driving a car bomb to his own hotel, where the target is a bigoted Protestant cleric a` la Ian Paisley, while Moira is held hostage in their home to ensure his cooperation and silence until the bomb goes off. Having parked the car, he now has a few minutes in which either to call the police or let the bomb kill its target and dozens of innocent guests.

As a balancing act of suspense and seriousness, this opening is worthy of Graham Greene -- an ordinary, decent man is presented with a simple, deadly and intractable moral dilemma. It is a testament to Moore's skill as a novelist that Dillon's decision whether to call the police or not complicates and is complicated by his marital difficulties. It is further testament to Moore that having made this decision, Dillon is faced with yet another one, which threatens his own life. Thus does Moore capture the tenor of life in embattled Belfast, in which not only a decision, but the failure to decide, or even putting a decision off, can have the most harrowing repercussions.

A native of Belfast who now lives in Southern California, Brian Moore writes with authority and compassion, as well as with the economy and confidence of a veteran novelist (The Lonely Passion of Judith Hearne, The Luck of Ginger Coffey, Black Robe), about middle-class life in Belfast. More than once Dillon, and through him, presumably, Moore himself, reflects upon the irony of living a comfortable middle-class existence in a place the world identifies with a gritty, brutal terrorist war. Despite the security measures that are by now part of daily life in Belfast, Moore makes the telling point that the struggle in Northern Ireland is the preoccupation of a violent minority, that many, if not most, people there have no compelling interest in the outcome. Indeed, much of Belfast knows the struggle only from television, like the rest of the world.

Yet Lies of Silence is finally something of a disappointment. The first half is taut, but the second half seems busy and slack, much rushing about to little dramatic effect. Further, the moral dilemma of the second half is really just a replay of Dillon's first decision, and its resolution, though frightening, is unsatisfactory. At best, during the suspense sequences, the writing is lean and evocative, but more often it is merely perfunctory and uninspired, a means simply of moving the characters from one place to another. And although Moira and several minor characters -- particularly Dillon's parents and a seedy IRA priest -- are vividly rendered, Andrea and Dillon are ciphers, thinly imagined and written. Andrea is simply the Younger Woman, while little is made of Dillon having once been a poet, an occupation that has a special place in Irish life. Indeed, Dillon seems a little dim to be the successful manager of a large hotel; the reader guesses the target of the bomb plot some 30 pages before Dillon does.

In the end, the failure of Lies of Silence is largely its failure to engage fully the difficult political and moral questions it raises. Ordinary life is defined here as middle-class life, and it's hard to escape the feeling that Moore disapproves of the IRA not so much because they are violent, but because they are working-class and vulgar. Unlike Bernard MacLaverty's Cal and the work of Belfast playwright Anne Devlin, in which the various dialectics of Belfast life -- Protestant versus Catholic, middle class versus working class, peaceful activism versus terrorism -- are embodied in the stories themselves, Lies of Silence presents a middle-class view of the IRA as an implacable, unreadable force like the weather, ruthless, largely faceless and monolithic, more a force of nature than a terrorist organization with a complicated internal politics.

Although Moore pays lip service to the continuing suffering of Belfast's poorer residents, finally he does not do justice to the insane complexity of the situation in Northern Ireland. The ordinary victims of life in a war zone are not necessarily the comfortable suburbanites who suffer occasionally, though tragically, at the hands of terrorists. Rather, they are the residents of the Catholic and Protestant ghettoes of West Belfast who are forced every day of their lives to choose between the humiliations of poverty and injustice on the one hand and, on the other, the support of a brutal struggle carried on in their name by violent men they did not elect. James Hynes is the author of "The Wild Colonial Boy."