Comedy and Romance as a Happy Couple : A SPANISH LOVER by Joanna Trollope; Random House $22, 334 pages

The cliche about the English is that they are good at compromising, at muddling through. This may or may not be true in general, but Joanna Trollope’s “A Spanish Lover” suggests that it has some relevance to literature. In most American novelists’ hands, the romance and the domestic comedy are separate genres, even antagonistic ones; but Trollope manages to combine them.

She does this by having twin sisters follow divergent paths. Lizzie Middleton has a husband, four children, a thriving art gallery business in Bath and a splendid 18th century house, the Grange. She believes in “being fulfilled. Using all the capacities you have, emotional, physical, mental. Filling yourself up.” And by this standard, she seems an unqualified success.

Frances Shore, in contrast, seems to have failed. In her late 30s, she is still single. Reticent and dreamy, she has drifted from one makeshift job or relationship to another. Her mother, Barbara, an outspoken feminist who once abandoned her family for 10 months to join the hippie scene in Marrakesh, pronounces: “Frances will never come to anything.”

Trollope, who has written several other contemporary novels (“The Choir,” “The Rector’s Wife”) as well as historical fiction, begins this book with a vision of almost Dickensian coziness. It’s Christmas. A tired but triumphant Lizzie is filling herself to the brim despite her parents’ quarreling and the demands of the children, each sharply and humorously individualized. Frances is expected to arrive soon, as she does every year.

Then comes a shock: Frances isn’t coming. Instead, she is flying to Seville, Spain, to dicker with a hotel owner about tours she hopes to book for her fledgling London travel agency, Shore to Shore.

Lizzie reacts with a vehemence that surprises even herself. Frances hasn’t just deserted the family at a traditional time of gathering; she has gone AWOL from her role in the family--that of the waif who makes everyone else feel secure.

When Frances comes back glowing, having fallen in love with the Spanish hotel magnate, Luis Gomez Moreno, who is Catholic and permanently, if unhappily, married, Lizzie’s concern turns to consternation.

An economic downturn hurts business at the gallery, forcing the Middletons to sell the Grange and Lizzie to accept a low-paying job as a school secretary. She and her husband, Rob, snap at each other. What Lizzie fails to acknowledge, though is that her real problem is a raging envy of her sister.

The repercussions spread wider. The twins’ father, William, has carried on a 25-year affair with a bohemian potter, Juliet Jones. A lovable ditherer, he has managed to avoid having to choose between women, just as Juliet has managed to sidestep domesticity.

All these arrangements begin to seem tawdry and fragile in the light of Frances’ newfound decisiveness. The final blow comes when Frances, bent on following “where the light beckons,” has Luis’ baby. Over his furious objections. In Spain.

At the mountain posada in Andalucia where Frances and Luis first become lovers, she notes that the hotel needs to install deck chairs “in which to read fat novels . . . as necessary to a certain type of English tourists as marmalade for breakfast.”

“A Spanish Lover” is just such a novel. Its fatness--its leisurely pace, its accumulation of scenic and social and psychological detail, its slices of dialogue as crisp as cucumber sandwiches--isn’t the kind to bloat deck chair readers unduly. It will just fill them up.

The romance, in the end, isn’t as successful as the comedy, largely because Trollope can’t make Luis, a bundle of stock Iberian charm and inhibitions, as real as those Middleton children. The story closes with a bit of a thud. Still, this is sophisticated entertainment of a sort we in this country seldom get a chance to sample.