With “Spider-Man” already a box office phenom, online movie ticketing services are gearing up for the next blockbuster: Both AOL Moviefone and Fandango have already begun selling tickets to “Star Wars: Episode II — Attack of the Clones,” two weeks before it bows May 16.

One reason is that online sales for tickets to “Spider-Man” bested expectations across the board, providing the first major sign that the Internet actually helps fill movie theater seats.

Fandango, for example, generated $3 million in ticket sales to the comicbook actioner, or 2.6% of the pic’s weekend B.O. On Thursday, the company sold one ticket per second for the pic. Fandango began selling “Spider-Man” tickets three weeks before its bow. Moviefone and Movietickets.com declined to provide “Spider-Man” sales figures.

” ‘Spider-Man’ sales climbed daily for nearly three weeks, topping our 2002 numbers and propelling record-breaking sales for one day,” said Art Levitt, prexy and CEO of Fandango.

Fandango offers tickets for close to 600 theaters with 7,200 movie screens at six exhibitors nationwide: Carmike Cinemas, Century Theaters, Cinemark Theaters, Edwards Theaters, Loews-Cineplex Entertainment and Regal Cinemas. Company enables consumers to print tickets at home, eliminating the need to wait in line at the box office.

Jupiter Media Metrix estimates that moviegoers will spend $257 million buying movie tickets online this year, repping 3% of the overall movie ticket market. By 2006, those figures are expected to grow to $644 million, or 7% of the market.