Yesterday. The Beatles are back. Or rather, their collective ghost will be resurrected at a three-day convention of Beatle-maniacs starting today at the Bradford Hotel, 275 Tremont St. in Boston. The whole thing is being put together by a 27-year-old full-time Beatle-maniac named Joe Pope, who spends the year editing a magazine called Strawberry Fields, roaming all over the country searching for Beatle memorabilia, and revving up for the annual convention. A few years ago, Pope had the idea of giving a party for a few of his friends who were heavily into the Beatles, but the thing has grown to such proportions that 3000 people came last year and Pope says he expects 4000 this year.

Festivities open tonight at 8 with a dance--music provided by two live bands who play nothing but Beatles tunes. Tomorrow there's an auction of all the T-shirts, buttons, posters, etc., that Pope's been collecting, followed in the afternoon by a series of guest speakers. You can hear author-photographer Jurgen Vollmer reminisce about the days when the Beatles were Teddy Boys in Germany, or listen to Richard DiLello talk about what it was like to be an office boy at Apple, Ltd. And if that's not enough, you can feast your eyes and ears on eight solid hours of unreleased Beatle films.

The boys themselves probably won't put in an appearance in the flash, though Pope says they've all been invited. And it probably would be a letdown anyway--they're not the same old boys any more. As Pope says, "it wouldn't be as good if they got back together again. They've all grown in different directions. It just wouldn't be natural."

But that doesn't mean you can't recapture your youth and theirs. A weekend ticket costs $12. Call 643-1994 and Joe Pope will tell you all about it.