Challenging the Acquiescence of Ulster : LIES OF SILENCE <i> By Brian Moore (Doubleday: $18.95; 200 pp.) </i>

It is all there, perhaps too plainly there, in the title. Brian Moore has written an angry political novel that is also a novel of suspense. The suspense is intricately tangled in an impossible moral choice, faced by a Northern Irishman who struggles to resign from his country’s conflict, and cannot.

Impossibility is the curse of the politics that has made Ulster’s history a strangled gyre that grinds away, decade after decade, sinking but never sinking through. And it is the focus of Moore’s anger.

Moore is a prolific novelist who has written on a variety of themes since he got out of his native Belfast, young, in 1948. Belfast--Catholic Belfast, specifically--is not out of him, though. “Lies of Silence” is his phrase for the mental and moral excusing and evading that allow the Irish Republican Army to operate out of the Catholic community, even though Catholics will deplore its violence, or at least, the seeming hopelessness of its violence.

Acquiescence in the face of evil is the charge Moore brings against the minority population of the North. He barely mentions the Protestant majority, and the British appear only in the form of a cool and barely glimpsed security official. The author’s quarrel is with the sentimentality that allows his Catholics to wink at present atrocities in the name of past heroics. His target is Mother Machree. She’ll kill you, the message goes; and in “Lies of Silence,” she does.

Michael Dillon is civilized and apolitical, the successful manager of a Belfast hotel that is owned by an American chain. He hopes for promotion to one of the chain’s London hotels; he cannot wait to get out of the city he was born and reared in.

London means a decent life and escape. Escape, also, because he will leave Moira, his gloomy and sub-hysteric Belfast wife, and go live with uncomplicated Andrea, a researcher for the BBC. Escape, finally, out Europe’s last medieval war, and into Europe of the Common Market and no-fault history.

Just as Michael is about to take off, his house is seized by an IRA gang. With Moira as their hostage, and under threat of death, Michael must drive a bomb-rigged car into his hotel parking lot--as manager, he will not be searched--where a time-device is to detonate and kill a lot of people, including an Ian Paisley-like Protestant extremist who is attending a lunch.

“Lies of Silence” is tightly, sometimes breathtakingly, constructed around the dilemmas that ensue. If Michael warns the police, he threatens Moira’s life. If he does not, he risks the lives of dozens of others. (One of the ingenious half-turns on this dilemma is that he cannot be sure if there is a dilemma. The IRA itself may or may not have given a warning; his captors will not say.)

The painful but undoubtedly correct choice is to sacrifice one life--perhaps--instead of many--perhaps. Except that Moira’s death would also be highly convenient. And Michael twists in the arid scruples of choice and conscience of a sort that Graham Greene wrote about more finely in “The Heart of the Matter” and “The Power and the Glory.”

It is Moore’s skill to give a living answer to this moral puzzle. No normal human being, much less a scrupulous one, could abide doing nothing, however finely balanced the choices. The hotel is bombed; its guests are evacuated in time.

A moral dilemma, however, now turns political as well. Moira, too gruesomely whiny up to now to matter much, suddenly becomes real. She and Michael, Catholics but uninvolved, must make new choices. He will go to London, the longed-for escape now justified by police warnings that he is in danger.

Moira, on the other hand, refuses “to let them push me out.” She will stay and denounce the IRA on television. In the book’s most effective confrontation, she lets Michael know that if he was willing to see her die to stand up against the terror, she is willing to lose him to another woman to do the same thing.

Even in London, though, Michael is not free. He had recognized one of the gunmen; the police ask him to make the identification. A priest with IRA connections comes over, ostensibly to plead mercy for the son of a parishioner. “A lovely woman,” he calls her. As for the youth: “You know what these lads are like, they’re just kids.” As if mercy were all that was at stake, and the duty of any Catholic, even a sophisticate, was to exercise it exclusively with other Catholics.

But the priest brings an unspoken message as well: The IRA will kill Michael if he talks. And he must decide finally whether he can escape the war and its choices.

In a number of ways, “Lies of Silence” succeeds remarkably. On the level of sheer suspense, for example. It is marvelously canny. And if there is contrivance in using this suspense, and the dilemmas that nourish it, to open up a larger political and moral dimension, it seems well justified.

Moore will be criticized for making his exclusive targets the IRA and the failure of most Catholics to confront the kind of choice that Moira and Michael are brought to. But he is not writing an overview of Northern Ireland; he has chosen, as is his right, to focus upon one aspect of its tragedy. If the chicken of majority oppression has laid the egg of minority violence--which, in turn, hatches a violent Protestant chicken, and so on--why, Moore has decided to tell an egg story. He tells it well.

On the other hand, he can be plodding in his prose. When Michael and Andrea arrive in London and enjoy a few days of happiness, Moore writes: “They were here. Everything had changed. Everything.”

He can also be crude in his characters, manipulating actions and discourse to make political points. The priest is oily and repulsive. Moore has cast a role instead of writing a character.

It is all too convenient when Michael, driving the bomb-rigged car after the night of terror in his hijacked home, passes the Catholic school where he was taught to hate Protestants. It was “run by priests whose narrow sectarian views perfectly propagated the divisive bitterness which led to the events of last night.”

As the protagonist, Michael has moments of real substance when he truly embodies the dilemmas he is in. But he is given too much to do, to feel, to think; the agony that is the heart of the book is a busy agony, and the busy-ness weakens it.