LOS ANGELES (Reuters) - For the second consecutive weekend, a major Hollywood film fell short of expectations at the box office on Sunday, providing a wobbly start for the lucrative summer moviegoing season in North America.

Walt Disney Co's "The Chronicles of Narnia: Prince Caspian," the second film in a series based on the "Narnia" books by C.S. Lewis, opened at No. 1 with estimated three-day sales of $56.6 million, the company said.

Industry analysts had expected an opening in the $80 million range, and certainly a figure above the $65.6 million start for the film's 2005 predecessor, "The Lion, The Witch and the Wardrobe."

The opening was nowhere near as disastrous as that for "Speed Racer" last weekend. Warner Bros. Pictures' $160 million kids flick crashed to a dismal $18.6 million during its first three days.

The summer season, which accounts for about 40 percent of the industry's annual sales, kicked off two weekends ago with Marvel Entertainment Inc's surprise smash "Iron Man," which has earned $222.5 million to date.

"Prince Caspian" stars newcomer Ben Barnes in the title role as a valiant warrior who joins forces with the four Pevensie children from the first film to battle an evil uncle. Both films were directed by New Zealander Andrew Adamson, a veteran of the "Shrek" series.

Critics were less enthused by the new film, with 66 percent of top reviewers giving their approval, according to Rotten Tomatoes (http://www.rottentomatoes.com), a Web site that collates reviews. The first one garnered a 78 percent rating.

The "Narnia" series is co-produced by Walden Media, a film company owned by Denver billionaire Philip Anschutz. Work is under way on a third film, "The Voyage of the Dawn Treader," with British documentary veteran Michael Apted stepping in for Adamson, who will serve as a producer.

Next up for moviegoers is director Steven Spielberg's high-wattage adventure "Indiana Jones and the Kingdom of the Crystal Skull," which opens on Thursday in time for the four-day U.S. Memorial Day holiday weekend. The film, long shrouded in secrecy, screened for excited journalists at the Cannes Film Festival on Sunday.

"Indiana Jones" will be distributed by Viacom Inc's Paramount Pictures, which is also handling "Iron Man" for Marvel. Warner Bros. is a unit of Time Warner Inc.