LOS ANGELES  Now comes the part where Indiana Jones dangles over the snake pit of public opinion.

Actually, a handful of Web reviewers have already struck at the film “Indiana Jones and the Kingdom of the Crystal Skull,” despite an intense effort by the director Steven Spielberg, the executive producer George Lucas and Paramount Pictures to keep this highly anticipated sequel out of sight until Sunday, May 18.

On that day, this fourth Indiana Jones movie is scheduled to make its debut at the Cannes Film Festival with an afternoon press screening, and another one at night.

At about the same time, the picture, which opens in theaters on the following Thursday, is expected to be screened for the news media and industry insiders at multiple showings in Manhattan and Los Angeles, while other screenings are scheduled around the world.

Mr. Spielberg is unusually fastidious when it comes to protecting his films from advance word that can diminish excitement or muddy a message planted by months of carefully orchestrated publicity and expensive promotions (including, in this case, a February cover article in Vanity Fair, complete with Annie Leibovitz photos of the cast, and leather bullwhips delivered weeks ago to newsrooms).