Writer A.S. Byatt won Britain's prestigious Booker Prize yesterday for her fifth novel, "Possession: A Romance," a tour de force of literary mystery and invention.

The Booker, which in its 21 years has become Britain's most coveted literary award, has proved to be a bankable honor, with sales of the winning book registering a marked uptick after the prize is announced. Some of that magic rubbed off on Kazuo Ishiguro's "The Remains of the Day" on this side of the Atlantic, too, when it won the Booker last year.

The $40,000 prize was announced at a banquet last night in London's Guildhall, and comes three days before Byatt is to receive this year's $42,500 Irish Times-Aer Lingus prize for international fiction.

Until 1983, when she turned to writing full time, the 54-year-old Antonia Byatt was a senior lecturer in English and American literature at University College, London. In addition to her four earlier novels -- "Shadow of a Sun," "The Virgin in the Garden," "The Game" and "Still Life" -- she also has written a scholarly book on Iris Murdoch and another on Wordsworth and Coleridge. Her novels are known for their literary allusions and academic preoccupations.

This year's Booker Prize winner is married, the mother of three daughters, and the older sister of novelist Margaret Drabble.

Five judges deliberated for two hours before "Possession" was chosen in a majority vote. They said they had been "unanimous, however, in agreeing that the standard of the other five novels was exceptionally high and this made their decision unusually interesting and unusually difficult."

The other titles on the short list, chosen from a list of 113 books published in the United Kingdom in 1989, were Penelope Fitzgerald's "The Gate of Angels"; John McGahern's "Amongst Women"; Mordecai Richler's "Solomon Gursky Was Here"; Brian Moore's "Lies of Silence"; and Beryl Bainbridge's "An Awfully Big Adventure."

Critics in Britain have raved about "Possession." In London, the Times said Byatt "entwines the wit of a satirist with the philosophical preoccupations of a rootless, godless 20th century writer. She combines the drive of the thriller with the measured exploration of human nature more normally associated with the 19th-century novel." The Times Literary Supplement was bold to say only a few months into the decade that the book "bids fair to be looked back upon as one of the most memorable novels of the 1990s."

In the United States, where Random House will publish the book Oct. 31, Publishers Weekly called it "a nearly perfect novel," and Washington Post critic Michael Dirda, in his accompanying review today, evidently concurs.