The Troubles Without the Irish--or the British : FATHER AND SON <i> by Peter Maas (Simon & Schuster: $17.95; 316 pp.; 0-671-63172-1) </i>

If writing can be described as exercise, then fiction and nonfiction use two different sets of muscles. And while Peter Maas, author of “Serpico,” “The Valachi Papers” and “King of the Gypsies,” clearly has the conditioning to succeed in nonfiction, novels are something else again. “Father and Son” is Maas’ eighth book, but only his second work of fiction, and while it is far from flabby, no one but his agent (to whom the book is dedicated) would characterize it as being in terrific shape either.

“Father and Son” is a novel that in simpler times would have been described as having been “ripped from today’s headlines.” It opens with an expertly planned break-in at a National Guard Armory in the Boston area and the subsequent pilfering of M16 rifles, grenade launchers, heavy machine guns and the like. The grateful recipient of this largess is to be the Irish Republican Army, which plans to use it to further its perennial struggle to free Northern Ireland from British control.

Getting the weapons is one thing, getting them to Ireland something else again. Here the IRA relies on what Maas portrays as a fairly extensive network of American supporters, both inside the federal government and out. One of them turns out to be a 19-year-old Harvard student and ace sailor named Jamie McGuire who, having been fed tales of Irish resistance by his grandfather, is recruited by an IRA lad who hears him sing teary songs of the rebellion like “Back Home in Derry” and “Kevin Barry” at a Cambridge pub.

Well, before the IRA makes contact with Jamie, however, a good 10 years earlier in fact, we meet him and his father, Michael McGuire, a New York advertising man with little or no feeling for his Irish heritage. What Michael did care about was his wife, Mary Alice, and a good part of this book is taken up with her unexpected death when Jamie was 9. We get to see how both father and son coped with the loss and how their relationship leads both to Jamie’s involvement with the IRA and his father’s attempt to insure that that attraction not be fatal.

As you would expect from a nonfiction writer of his caliber, Maas handles that initial armory break-in scene quite nicely. In fact, all the situations involving the logistics of IRA covert actions both in this country and on the Emerald Isle, as well as the machinations of the British counterintelligence operatives, are brisk and involving.

Maas has clearly done quite a bit of research in this area, and it pays off not only in enticing tidbits like how IRA operatives are snuck past U.S. Customs and exactly the way razor wire is used to protect British installations in Belfast, but in a general air of authenticity that makes the plot of “Father and Son” that much more believable.

Maas is also good at capturing the determination and resilient spirit of the IRA, the timeless feeling that, as one of its leaders says, whatever he accomplishes in getting the British out is “but a tick of the clock that’s been runnin’ over eight hundred years.” Maas manages to sympathize with the lads without fawning over them, and though that may keep the book off of Margaret Thatcher’s bedside table, it is a virtue nevertheless.

But at home as he is in the tension and logistics of secret missions, that’s how off base Maas is in the delineation and development of character. It’s not just that his Britishers literally say things like “Chin up, old chap” and “Cheerio,” or that his IRA leaders are all noble and laconic: In the context of a straight thriller, those lapses are acceptable, even to be expected. However, Maas is attempting something different with “Father and Son” and that simply does not come off.

What Maas is trying to do with Jamie and Michael McGuire is create realistic, believable human beings, not only because the more we care about them the more effective the jeopardy he puts them in will be but also because he knows that character is the key fiction muscle that needs to be developed if a novel is to rise above the level of the potboiler.

So we are forced to wade through what feels like endless scenes of father and son, often fishing but always exchanging tiresome bromides about life. Though he is deft when it comes to action, Maas has a hollow tin ear when it comes to dialogue, and emotionally bankrupt lines like Michael’s thought that “If a bad thing happened to Jamie, he didn’t think he could go on” lie listlessly on the page like so many dead flounder.

Not only doesn’t this attempted humanizing of Michael and Jamie add to the book’s considerable suspense, it almost diminishes it, because every time Maas cuts away from action to character you want to get up and have a beer. The idea of trying to escape from the cliches of genre is a good one, but Maas’ insufficient efforts have ended up only underlining them.