FARRAR, STRAUS once sent out a press release which referred to Edmund Wilson's Dairies, but that was easily rectified, with a follow-up note ("Mr. Wilson does not keep cows"). Making amends is a little harder with 150,000 finished books, as in the case of Who Took Toby Rinaldi?, a light-hearted thriller by Gregory Mcdonald just reprinted by Dell. "They misspelled my name 30,300,000 times," he asserts, not amused--although "Book Report" tried for its own total and came up with a figure just over half that. Whatever the final number, that's a lot of error. How did he discover the mistake, which has him identified as "Gregory Mcdonaly" on the running head, at the top of the left-hand side of each pair of facing pages? "My son found the book in the local store and brought it home to me, announcing that he guessed we were going to have to change our name," Mcdonald says wryly.

Since that heart-stopping moment, the chairman of the company has apologized to Mcdonald, but the official word, as repeated by Isabel Geffner of Dell, is that only in the event of a second printing will that "y" be banished and the "d" restored. Mcdonald, meanwhile, has a consolation that other authors in a similar situation might be denied. Creator, in paperback originals, of the characters Fletch and Flynn, he's just published two new titles each featuring one of these popular heroes: The Buck Passes Flynn (Ballantine) and Fletch and the Widow Bradley (Warner). Of this last, Mcdonald says, "It's a real do-not- reveal-the-ending book," and it's already made several of the paperback best-seller lists. "I've got so many books out at one time I feel like Barbara Cartland." At least he doesn't feel like Beverly Sills, who saw the word "public" misspelled (the "l" got dropped) on the very first page of her 1977 autobiography, Bubbles.