Heavy-hitter film figures Steven Spielberg, George Lucas, Harrison Ford and Shia LeBeouf are on the Big Island filming the fourth installment of the "Indiana Jones" franchise.

It's possibly the worst-kept secret along the Hamakua Coast north of Hilo, where residents are buzzing while studio officials remain mum about the invasion of Indy & Co. over the next three weeks.

While the film project doesn't yet have an official name, titles in circulation include "Indiana Jones IV," and sometimes "Indiana Jones and the City of Gods." The whip-whacking action hero battles Russian soldiers near a Hamakua waterfall for the film's opening sequence.

The film's budget is an estimated $125 million.

Spielberg, who has directed three "Indiana Jones" films, is back at the helm. Lucas, the creator of the "Star Wars" legacy, is an executive producer who also contributed to the story line. Lucasfilm Ltd., the production company, has opened an office in sleepy Hilo.

"They're insisting on using 'The Untitled Genre Project' as a title, putting us in an awkward position," said Donne Dawson, Hawai'i film commissioner, who confirmed the Big Island presence of Spielberg's production.

The film, which started production earlier in Deming, N.M., will be distributed by Paramount Pictures for an expected May 2008 release.

Several hundred Island extras showed up at a recent casting call, Dawson said.

Ford and Spielberg are no strangers to the Islands. Spielberg filmed sequences on Kaua'i for the first movie in the series, "Raiders of the Lost Ark," in 1980. The director shot portions of three "Jurassic Park" features — "Jurassic Park," "The Lost World: Jurassic Park" and "Jurassic Park III" — on Kaua'i. Footage for "Jurassic Park III" also was shot on O'ahu and Moloka'i.

Ford filmed "6 Days/7 Nights" on Kaua'i in 1997.

LeBeouf, who starred in this year's successful "Disturbia," and was on O'ahu for the "blue carpet" premiere of the animated "Surf's Up," for which he voiced the lead penguin's part, appears in the latest "Indiana Jones" installment as a rebel motorcycle rider — the son of Jones and Marion Ravenwood.

Karen Allen, who played Ravenwood in the first film, is in the cast, which also includes Cate Blanchett, Jim Broadbent, John Hurt and Ray Winstone. It was not certain if all actors would be on the Big Island for filming.

Spielberg's company, DreamWorks, also is filming "Tropic Thunder," with a $100 million budget, on Kaua'i. Ben Stiller stars and is directing a comic story about actors doing a war movie who unexpectedly face real fighting. Locals available for employment on or off camera have had to select one or the other project.

"Extras and tech crews had to make choices," Dawson said. "It's a good problem to have."

Dawson said the Kaua'i and Big Island projects are expected to contribute to the state's $126 million in projected filmmaking expenditures this year.

"It's cyclical, so when it rains, it pours," she said of the overlapping projects.

A record-setting $164 million was spent in Hawai'i on film projects in 2004, when four television series were shot on O'ahu: ABC's "Lost," NBC's "Hawai'i," Fox's "North Shore" and Warner Bros.' "Rocky Point."

"Indiana Jones" on the Big Island and "Tropic Thunder" on Kaua'i are benefiting from the state's tax-credit incentives, Dawson said. Neighbor Island shoots provide 20 percent refundable production tax credits, compared with 15 percent on O'ahu.

Meanwhile, "Lost" — now in pre-production at the Hawai'i Film Studio on the slopes of Diamond Head — will launch its fourth season shooting schedule on Aug. 20.

Reach Wayne Harada at wharada@honoluluadvertiser.com.