THE OPRAH EFFECT

Once an author commits to being a guest on Oprah Winfrey's Book Club, it's likely that his or her name will be irrevocably linked with that of the famed host. In fact, until the Oprah discussion airs, all of the author's other media appearances must pass muster with the show's production outfit, Harpo. ''It's in the contract,'' one publisher's spokeswoman said. But who's complaining? As far as sales spiking goes, nobody does it better than Oprah. Take in the following numbers:

-- Alexandra Jacobs

THE DEEP END OF THE OCEAN by Jacquelyn Mitchard (Viking)

Date announced: Sept. 17, 1996

Copies in print before announcement: 100,000 Copies in print to date: 915,000

SONG OF SOLOMON by Toni Morrison (Knopf; Plume; Signet)

Date announced: Oct. 18, 1996

Copies in print before announcement: 1,374,000 Copies in print to date: 2,784,000

THE BOOK OF RUTH by Jane Hamilton (Houghton-Mifflin; Anchor Books)

Date announced: Nov. 18, 1996

Copies in print before announcement: 93,000 Copies in print to date: 1,160,000

SHE'S COME UNDONE by Wally Lamb (Washington Square Press/Pocket Books)

Date announced: Jan. 22, 1997

Copies in print before announcement: 147,000 Copies in print to date: 1,217,000

STONES FROM THE RIVER by Ursula Hegi (Simon & Schuster)

Date announced: Feb. 28, 1997

Copies in print before announcement: 165,000 Copies in print to date: 1,415,000