WHEN IT COMES to inventive plotting, it's hard to beat the intrepid popular novelist, constantly scheming to unglue potential readers from the latest TV miniseries -- or, better yet, inspire one. But when you get right down to it, the most successful practitioners are usually just finding new variations on tried and true formulas: the Machiavellian family squabble, the thwarted romance, the battlefield epic.

Since the theory that less is more hardly ever operates on such turf, all these themes are often tossed in together, as is the case in five of the latest candidates for the bestseller lists. Each one features a story of family life and love (occasionally happy, usually not) played out against the background of some of history's nastier wars. THE LOVING CUP. By Winston Graham. Doubleday. 440 pp. $17.95.

IT'S been years since television's "Masterpiece Theatre" said goodbye to Ross and Demelza Poldark, the dashing Cornish mine owner and his charmingly boisterous wife, who always managed, just in the nick of time, to escape the machinations of their archenemy, filthy rich banker George Warleggan. In the interim, Winston Graham has been spinning out their story to the next generation in novel after novel. This one, the 10th in the series, takes place from 1813 to 1815, as Napoleon and Wellington are skirmishing across Europe. Ross' nephew, Geoffrey Charles, is all grown up, an officer in the Peninsular Army and the new husband of a Spanish noblewoman. Not to be outdone, Ross' own son Jeremy will soon follow in his cousin's footsteps, although his romantic fortunes (scuttled by his passion for an unattainable aristocrat) seem much less promising.

Back at home, the now middle-aged Poldarks and Warleggans continue to scrap, although the person who could suffer most from the fallout is lovely Clowance Poldark, who's become very fond of a handsome but disreputable smuggler whom George Warleggan may just manage to trap -- if he isn't too busy feuding with his own ne'er-do-well son, Valentine.

Winston Graham writes beautiful descriptions of Cornwall and has a knack for creating wonderful bit players. And he can twist a plot as well as anyone. Still, this isn't a book for the uninitiated, since it continues a lot of the action begun in its predecessors and leaves plenty of threads hanging for the next installment. On the other hand, what true believer can resist wondering whether Ross will become a baronet, whether the Poldark family will decamp to Paris -- and whether its youngest daughter, Isabella Rose, will turn out to be even more of a handful than her mother once was? AN EXCESS OF LOVE. By Cathy Cash Spellman. Delacorte. 526 pp. $16.95.

MARTYRS are what we do best in Ireland," broods Seaneen O'Sullivan, one of the heroes of this lushly written saga of love, rebellion, and civil war. It's also what author Spellman does best, since few of her characters emerge unscathed from the 1916 Easter Rising and its bloody aftermath.

The family at the center of the drama is a wealthy Anglo- Irish one, the FitzGibbons. Papa, a starchy widower, soon fades from the picture, but the three children -- Con, Beth, and Desmond -- are all, as one observer puts it, "seduced by Ireland." Con abandons her class to marry a poet activist called Tierney O'Connor; Beth compensates for an unhappy union with the Earl of Sligo by writing feminist novels and falling for one of the leaders of the Irish Republican Brotherhood, and Desmond turns his diplomatic contacts to the service of gunrunning.

The story is narrated by Beth, with intercuts of scenes that follow the other characters. This device occasionally turns cumbersome, as do some of the more unlikely developments of the plot, particularly when the action moves along to the alliances and rivalries o Beth and Con's children, who manage to represent every shade of the political spectrum. But Spellman's graceful, atmospheric style of writing usually compensates, and the vast audience that gobbled up her previous bestseller, So Many Partings, will no doubt be willing to take things as they come.

Certainly they'll get plenty for their money: the gore of street battles and the glamour of the theater; jail breaks and secret trysts; spies and safe houses; women at the barricades and men on the run. There are even cameo appearances by the likes of William Butler Yeats, Maud Gonne, Eamon de Valera, and Winston Churchill.

"Heroism is a thing of the heart," Beth declares, "not of the head." And that's the angle this novel exploits to the hilt. AFTER GOLIATH. By R.V. Cassill. Ticknor & Fields. 209 pp. $14.95.

WHAT'S a so-called serious novelist doing writing a historical potboiler? I dunno. And, I suspect, neither does he. Pat of the problem may be that after Joseph Heller's latest novel and Richard Gere's latest movie, After Goliath looks like just another Biblical rerun. But that still doesn't explain Cassill's odd blend of burlesque wisecracking and semipoetic descriptive fancies.

The tale of King David's family troubles is narrated by Joab, a salty old soldier who lolls under a fig tree dictating to Jehoshaphat, who in turn "hopes to get some of his present work included in the Bible." Joab gives us the lowdown on "the naughty stuff with Bathsheba, Absalom's rebellion, how we handled the traitors Abner and Amasa, and other famous matters I have knowledge of."

Joab claims that David "has entertainment value, which is the greater part of either history or religion," and it can't be denied that this slim pastiche of episodes is never boring. But it also seems fairly pointless -- except to serve as a vehicle for raunchy jokes. Joab's favorite victim is David's son, "that wimp Solomon," about whom he remarks, "Put a sling in this offspring's hand and he would have invented the brassiere."

In complaining about David's prophet, Nathan, who seems constantly to lapse into parables about sheep, Joab opines that "maybe Israel was far down in cosmic rating after all, a fit subject for B pictures, indeed." Readers of Cassill's novel won't be inclined to disagree. THE THREE PASSIONS OF COUNTESS NATALYA. By Alan Fisher. Macmillan. 350 pp. $15.95.

FISHER'S title is somewhat misleading, since his gorgeous Russian heroine is distinctly cool and imperious. Instead, the passion comes mainly from the three men who constantly dream about, periodically rescue, and frequently compete for her as the Tsar's empire comes crashing down all around them.

Michael Stern is a dour but honorable Englishman, an engineer whom the British authorities hope will work miracles on the decrepit Murmansk Railway, the only means by which they can supply the Russian arms rapidly crumbling resistance to the advancing Germans. Stern realizes the importance of all this, but World War I pales in comparison to a haunting incident from his past, which he thinks may link him to Countess Natalya Meretskova's dead brother. Also interested in the countess are a brutish Cossack general, Malnekov, commander of the Petrograd garrison, who has somehow managed to become her lover, and a Bolshevik revolutionary called Koltsov, who will one day have the power to save her from a firing squad.

Despite her trysts with Malnekov, the countess is a pretty cold fish. But what she lacks in liveliness is more than made up for by a supporting cast that includes a freewheeling American trader, an ambitious female university student, Stern's deadpan Finnish aide-de-camp, a lecherous professor doubling as a Duma politician, and a properly slimy secret policeman, who starts out working for the monarchy and easily glides into the Soviet Cheka.

The story they all inhabit, which recently won Britain's Georgette Heyer prize for historical novels, depends rather too strongly on magical coincidence, and the countess' only real contribution to the plot is to insist on remaining in revolutionary Petrograd with her sister and a wounded officer. This allows everybody to knuckle down for one big final confrontation -- and a flight across the frozen Baltic to an unlikely denouement. THE SNOW GODS. By Herbert Burkholz. Atheneum. 543 pp. $19.95.

BURKHOLZ'S story of three generations of Austro-American schussers has more unexpected turns than a whole season of slalom races. It begins in the winter of 1914 with two Tirolean farmboys, Anton and Otto Prinz, brawling over the girl who will wind up marrying one of them. And it ends in 1983 with the birth of Anton Prinz's great grandsom and namesake, whose conception has touched off the latest and deadliest round of violence in a family that takes its women and its skiing very very seriously.

The problem is that the Prinz men usually want the same women and the same skiing. This forces Anton to emigrate to Vermont, where he changes his name to Prince and manufactures skis in partnership with a stubborn Calvinist named Elizabeth Chandler. Back in Austria, brother Otto is also manufacturing skis -- and casually wiping out half a dozen friends on wartime maneuvers.

Already the lines have been drawn. Anton is the good Prince, and because of this he will have a son, nicknamed Digger, who becomes a legend in American skiing and a hero famous for his World War II exploits with the Yugoslav partisans. Otto is the bad Prinz, and thus he will turn into a wifebeating Nazi Gauleiter who tries to ruin his brother's business and blackmail his sister's husband. Otto will have two sons, one good and one bad. His sister Marta, an opera singer, will have twins who are, well, strange. And then Digger will have two boys, one a messed-up Vietnam vet and the other an Olympic skiier. And so on and so on.

By the time we reach the third generation, there are enough permutations and combinations to satisfy even the most jaded reader. Murders, explosions, decapitations, nymphomania, group sex. There's a little of almost everything. What there's a lot of are people who make the wrong choices over and over again. But, for some funny reason, you never get tired of watching them do it.