HOW ABOUT a doomed love affair between the

daughter of a Mafia boss and a sweet Puerto Rican kid just out of Harvard Law School? If it sounds a little like an updated West Side Story, and you can feel the heart-strings already tugging, that's the general idea. Jimmy Breslin is the proverbial tough guy with a quiver full of Cupid's arrows jammed under his bullet-proof vest. He is also a shrewd, funny, sardonic observer of big-city ways.

The result is a romantic novel with very sharp teeth. Dreamers and weepers will probably buy the somewhat improbable love affair, while buffs of the urban absurd and grotesque will applaud such prime Breslin touches as: New York's Finest throwing up all over the insides of a search helicopter and three Doberman pinschers who have undergone delicate throat operations that prevent them from making a sound before they kill.

Also credit Breslin with being one of the very few white/Anglo writers to plunge into the teeming underside of Manhattan Hispanic life. Italicized Spanish peppers his pages like buckshot--a little too conspicuously? --and middle-class readers get a scary education in the packaging and selling of huge amounts of heroin. It is all rough stuff. But Jimmy Breslin is a hard-hat troubadour who works heroically to find sunshine in the sleaze until the final eclipse, when his Puerto Rican hero is killed for the wrong reasons and nasty business as usual goes on in its cheerful way.

Breslin's authenticity as a writer is in his small details. He knows the cigarette-smoking anxiety of a cheating wife. He can show us lazy detectives bullying the helpless as if he once wore a shield himself. He is at home with all the unflashy, small-print realities of New York life: rigged political meetings to choose state supreme court judges, gangsters in the kitchen cooking lasagna, young Jewish lawyers "dressed in the clothes of old Protestants, vests and watchfobs." He is as observant as a cat. But this veteran newspaperman also has a booming romantic streak, in the tradition of vintage Manhattan tale-tellers from O. Henry to Damon Runyon, and he hangs all this encyclopedic knowledge on a plot that could serve for a hard-boiled operetta.

The prime mover in his fable is a lusty young bull from the Caribbean side of Puerto Rico who storms the East Bronx to take over the drug trade and be king for a day. His name is Teenager and his goal is to do for heroin what John D. Rockefeller did for oil. Under his wing is his pride and joy: the clean-cut, straight, upright Maximo Escobar, who through dint of hard work has put himself through Harvard Law and is about to embark on a beautiful career helping his people.

But all of this is changed forever when Maximo accompanies Teenager to a Mafioso's home across the Hudson River. Here, while the two bad guys split up the Bronx drug-turf, Maximo meets Nicki, the daughter of Boss Mariani. It's blind passion at first sight, folks, even though Nicki and all the Marianis normally despise blacks and Puerto Ricans as unthinkingly as they do odors from an open sewer. (Candid and jolting is Breslin's double-barreled bluntness about New York ethnicity: no group escapes, including the author's own Irish, "nearly all practicing the religions of Catholicism and slander.")

Anyway, Maximo and Nicki begin a perilous affair while she waits for her mob-guy husband to be released from jail. If her father ever finds out about it Maximo's head will decorate a caesar's salad down on Mulberry Street. In the meantime Teenager and Boss Mariani have fallen out over the spoils and had the other team's pushers murdered several times over. A contract goes out on Teenager and his henchmen. But the lusty bull who was the greatest street celebrity the East Bronx had ever seen is pinched instead by a vindictive, inept Irish detective, and his empire collapses. The way now seems clear for Maximo and Nicki--love has replaced simple bed-pounding, she has gutsily left her newly-sprung husband--when the back of the young lawyer's head is "turned into tomato soup" by a Mariani hit-man. For all his Harvard polish, Maximo is mistaken for just another Puerto Rican pusher. Curtain.

The bare bones above certainly don't indicate the thick swath of life Breslin gets into his prose, although the story-line clearly shows that this book is aiming for a wide, popular, bittersweet appeal. Breslin really hasn't had a deluxe fictional success since The Gang That Couldn't Shoot Straight in 1969. Whether he will be lugging all those money-bags down to the bank with this one is a thorny question, but essentially it comes down to how two different sets of readers are going to react.

Serious readers and connoisseurs of metropolitan black humor will savor much of the accurate, unflattering and sometimes savage observation in these pages; they will also sense something manufactured in the dutiful boy-girl scenes. Escapist readers, on the other hand, may very well be dismayed by the street-level rawness of the normal Breslin vision every time he gets away from the silk and satin Band-Aids of romance. Of course it's possible that a fresh generation raised without any illusions except the most famous--the salvation of romantic love--can take it all in without splitting their emotions. We'll have to wait and see.

Until then just let it be said that this reviewer, who sides with those who will value this novel for its iconoclastic truths of observation rather than its torchy centerpiece, wishes Breslin had tucked in more loose ends before releasing this book. A case in point is an 11-year-old boy who is raped in the Bronx children's jail. The boy tells Maximo that his rapist has threatened to kill him if his identity is revealed. The boy reveals it. But by then Breslin has gotten involved in his bread-and-butter love story once again, and we never know if the death- threat is attempted. It haunts us to the last page, because in these areas Jimmy Breslin knows things that we will never know and it's frustrating when he just flips them away like half-smoked cigarettes.