Woman of contrasts: Nancy Astor portrayed on PBS

George Bernard Shaw called her ''a recklessly unladylike lady.'' Winston Churchill said of her 25 years in the House of Commons that ''Parliament has never been the same since.''

''Masterpiece Theatre,'' too, may never be the same again after this venture into cultural soap opera, high-society brand.

Nancy Astor (Sunday, 9-10 p.m., Masterpiece Theatre, starting April 15 for eight Sundays, check local listings) is based on the Christopher Sykes biography of this Virginia belle who was the first woman to win a seat in Britain's House of Commons. Lisa Harrow, in the role of Nancy Astor, gives a superb performance as this cantankerous woman who seemed to have a tempestuous effect on the lives of everybody around her. James Fox, as Waldorf Astor, gives the character an overwhelmingly sympathetic reading.

''Nancy Astor'' the miniseries was as controversial as Nancy Astor the woman when it aired in Britain a few seasons back. Aside from the fact that the alleged Nazi-leaning Cliveden group is treated rather gently, the series revealed that Nancy's son Robert was jailed at one time for homosexual activities - something which had not previously been published in English newspapers due to the Astor influence. At the time of its showing, too, some Christian Scientists objected to the portrayal of Nancy Astor's rather simplistic and personalized interpretation of Christian Science, her chosen religion.

In fact, this miniseries is perhaps a bit more soap opera than most BBC shows. Even though it is based upon a respectable book, there is much delicate delving and ''dramatic license'' in episodes concerning Nancy Astor's disdain for sex in marriage and the intricacies of her various relationships with her husbands, children, and sisters.

The Nancy Astor portrayed here - a woman characterized by series host Alistair Cooke as ''vibrant, charming, thoughtless, generous, and outrageous'' - was a living contradiction: loving even as she was hateful, thoughtful even as she was thoughtless, generous even as she was penurious. The contradictions apparently made themselves evident in the way she practiced her religion. Alistair Cooke, host for the series, observes that many Christian Scientists would ''take exception to her bullying of non-Christian Scientists and berating of doctors.''

Whatever she did, however, she did with bombastic style. As scripted by Derek Marlowe and directed by Richard Stroud, ''Nancy Astor'' is brilliantly acted by a mainly British cast, which does quite well with Virginia accents as well as upper-class British speech and customs. Whether one loves ''Nancy Astor'' as an imaginative biographical blockbuster or finds it a slightly distasteful exercise in rewriting history (and both opinions have some validity) , the fact is that the miniseries is eight hours of entertaining dramatized history - or near-history.