THIS is a brave and artful novel disguised to appear safe and conventional. One can read on for some time as if it were simply a ''terror stalks the high seas'' thriller, but one would be an uncommon fool to do so for very long.

Joseph O'Connor, an Irish critic and playwright who is also the author of several previous novels, lures us into an easy read that, before we know it, becomes a chilling indictment not of a murderer but of us. As a London publisher says midway through the book, advising a writer unsuccessfully peddling his fiction, this is ''a good old thumping yarn,'' the sort of thing a reader can ''sink his tusks into.'' But ''Star of the Sea'' is also an agonizing inquiry into the nature of abandonment and the difficulty of finding anyone who will truly care about the fate of others. How large does suffering have to loom before we take notice? O'Connor suggests that we can tolerate mountains of misery, sipping our coffee and reading our newspapers as the corpses pile up beneath the headlines.

The Star of the Sea is a leaky old tub sailing from Ireland to New York in the terrible winter of 1847, carrying in its staterooms a reluctantly intertwined collection of characters. The most noteworthy is an Irish aristocrat, David Merridith, Lord Kingscourt, whose Oxford training has shown him ''how to put on like a cheerful idiot'' while he's got his ''hands sliding around your neck.'' Merridith and his family are being stalked by a man named Pius Mulvey, who has been charged, on pain of death, with executing the aristocrat before he reaches America. Mulvey's orders issue from a group of Irishmen who resent Merridith's eviction of his tenants, leaving them to starvation as he takes his bankrupt but very comfy self off to the New World.

Connected to both Merridith and Mulvey is a peasant woman, Mary Duane, who has cause to disavow the lot of them, and yet does not. In a world where abandonment seems the outcome of all human ties, Mary Duane remains true, against all reason. She alone seems poignantly but absurdly loyal. Her Cordelia-like heroism is alien to the novel's plot and thus a moving but pointless anomaly.

Also on board is a cargo of steerage passengers, ill and starving, on their way to what they trust will be a new life, or at least a life. Their chronicler is another passenger, Grantley Dixon, an American journalist who writes for The New York Tribune, a man possessed of a self-congratulatory voice of confident compassion. He records the horrors of the Irish potato famine and its million dead -- from starvation and from the callousness of Anglo-Irish landowners and English politicians. Dixon reports all this with a moral zeal that is as gratuitous as it is perceptive: ''To remain silent, in fact, was to say something powerful: that it never happened: that these people did not matter.'' Aware that these Irish peasants have died, as he puts it, ''in the dark,'' Dixon is also aware of both the sonorousness of his wordplay and the excitement it gives him to use it. Through this reporter, O'Connor shows how little speaking of such things can matter; Dixon's talk participates in the same self-regard as Merridith's, serving to shut out the rest of the world, especially those who might have some claim on their (and our) sympathy.

It is Dixon at his most assured who opens the novel with a chapter called ''The Monster,'' a drooling and wildly overwritten portrait of Pius Mulvey that allows us to believe, at least for a while, that we are in the midst of a comfortable melodrama, inhabiting a world so simple that terms like ''evil'' can be easily defined. But Dixon ends his slavering indictment of Mulvey with an admission that the monster is simply a useful fiction, providing ''the illusion of unity'' to a group only capable of binding itself together ''not by what it shares but ultimately by what it fears.''