SWAN'S CHANCE. By Celeste De Blasis. Bantam. 560 pp. $16.95.

THIS IS A down- comforter of a romantic novel, all padded with bits of historical research and just as easy to sink into -- though readers unfamiliar with its predecessor, Wild Swan, will possibly have some initial difficulty figuring out Alexandria Carrington Falconer's marital history and which children belong to which of her husbands. Aside from this little genealogical confusion, however, the only other challenge is staying awake in the face of De Blasis' earnest narrative style. Yet the final result isn't unpleasantly soporific, and if you snooze, you will probably dream of 19th-century Baltimore harbor scenes and graceful, prancing thoroughbreds, for the Carrington-Falconer fortunes are based on shipping and horse- breeding.

When the story opens, it is Maryland in 1836. One of the first things we learn is that the beauteous Alexandria and her equally handsome second husband, Rane Falconer, are the kind of decent folk who offer shelter on their estate, Wild Swan, to runaway slaves, and it's quickly obvious that the villains will all turn out to be the types who'd sell anyone handy down the river. By the time the book's over and the Civil War ended, numerous private and public catastrophes have been weathered, each contrasting the goodness of Alexandria and the badness of those who don't share her values. In short, Dallas this isn't, and if you like your Carringtons more supercharged, get out your television listings. JIAN. By Eric Van Lustbader. Villard. 448 pp. $17.95.

AT THE OPPOSITE end of the pop spectrum from the somewhat dull comfort of a Wild Swan or Swan's Chance are such roller-coaster rides as offered by The Ninja, The Miko and now Jian. Eric Van Lustbader is a sort of New Age Mickey Spillane, dishing out no sex without violence and vice-versa, all with an oriental twist. Each page almost writhes with the heat of his feverish imagination, and the number of quick cuts between cliff-hanging chapters keeps boredom definitely at bay. Maybe the formula wears thin, if you've read more than two of his novels, but you can't deny he delivers Sensation with a capital "S."

The stalwart hero of Jian is Jake Maroc, a half-American, half-Chinese secret agent based in Hong Kong, and, in the usual way of things, he's on the run from various enemies, including his own superiors. Yet more intriguing, really, is his would-be nemesis Nichiren, a viciously imaginative killer who shares with Jake a mysterious past that somehow controls the destiny of each. Ambitious Russian counterintelligence officers, crafty Chinese senior bureaucrats, the self-protective merchant traders of the colony, nervous American spymasters, plus assorted traitors: all have a stake in the proceedings, as the race to control Hong Kong's future accelerates. But none of them is exactly whom he seems to be, and part of the fun is watching Van Lustbader slowly unknot his lurid cat's cradle of a plot. TOO MUCH TOO SOON. By Jacqueline Briskin. Putnam. 477 pp. $17.95.

ALTHOUGH the Carringtons in Swan's Chance don't resemble their television "kin," the Crystal of this novel certainly brings Joan Collins to mind. Tough and ambitious and never above using her sex appeal to get what she wants, Crystal Sylvander steps on both her sisters in her upward climb and continues scrunching her heel in their faces as the story unwinds. But Honora, the older, and Joscelyn, the younger Sylvander daughter, eventually both keep enough distance from the scheming Crystal to allow a few separate plot strands to unfold.

In 1949, when the book begins, the Sylvander girls, along with their father, a posturing and ineffectual Englishman, are recently arrived in San Francisco from London. There they hope to take advantage of the largesse of their elderly, rich uncle, Gideon Talbott, head of a major international engineering firm. However, he's a horrid curmudgeon, to say the least, and the only way any of them benefits from the relationship is when Crystal marries him! Rivalry then becomes the dominant theme, between the women and the men (Honora's husband founds a competing company), and their children are not exempt from the bitterness.

Briskin, like another Jacqueline before her, isn't much for subtlety, but why should she be? But those who crave such prose as -- "Crystal gripped the Limoges washbowl. The peal-trimmed sweetheart neckline of her white velvet wedding gown revealed the sumptuous curves of her breasts, which rose and fell convulsively, as if she was sobbing. Yet there were no tears in her vivid blue eyes" -- will avidly follow the fates of three Sylvanders, their loves and fortunes. MISS GATHERCOLE'S GIRLS. By Judy Gardner. St. Martin's. 351 pp. $15.95.

THIS IS A WAN, if not totally unappealing, novel which follows the career of Cassica Marlow, born with the century and destined always to be make her own way in the world. After her parents die, leaving her penniless, she, like the Sylvander sisters, must turn to a wealthy uncle for help. But he denies her her own most cherished dream, to attend Cambridge's Girton College; his idea, instead, is that she take a year at a secretarial school, the Gathercole Commercial Academy in Liverpool, and this she finally assents to.

The problem is that, after this setback, Cassica just muddles on in a pretty ordinary way. Fiction about the commonplace existence of a young working woman in early 20th-century England isn't in itself a bad thing, but Miss Gathercole's Girls keeps sending out vague signals that some change is on the Brink of Happening to Cassica -- yet it never actually does. A tragedy befalls a hapless cousin she befriends, and one of her chums survives an encounter with white slavery. She has an on-again, off-again romance with a half-baked revolutionary, then falls in love with one of her employers, a middle-aged European composer who rejects her.

If all of these events were less flatly narrated, one might feel more compelled by Cassica's tale and be more charmed by the books' neat conclusion. As it is, Gardner's given us adequate rainy-day reading; on a sunny afternoon, though, its modest appeal would be thrown into sharper, and thus less flattering, relief. TWILIGHT CHILD. By Warren Adler. Macmillan. 295 pp. $15.95.

THE RIGHTS OF grandparents is the theme of this contemporary domestic drama. Frances, a young widow about to marry again, also decides at the same time to break with her former in-laws and deny them the chance to visit or even send presents to their only grandson, 5-year old Tray. Her reasoning is that she's entitled to a fresh start, unhampered by past ties; for Charlie and Molly Waters, though, it's not that they wish to interfere in Frances' new life, only that they passionately adore the boy and can't simply erase his importance to them.

After two years go by without a glimpse of Tray, the Waters have no choice but to take their case to court. They have little idea of the sort of public torment they're submitting themselves to. Lawyers and judges, the stubborn hostility of Frances and Peter, her new husband, strained relations with each other -- all of these factors catapult them into a world far more complicated than their simple blue-collar existence has prepared them for. But despite the fact that Adler gives them dignity and makes one care about their fate, it's really too much of a didactic, casebook sort of novel to be to everyone's taste.

Still, one very worthwhile element is the portrayal of a non-glamorous middle-aged couple with an affectionate, enduring marriage, who give each other strength throughout a trying ordeal.