LOS ANGELES — An incurable tinkerer, Warren Beatty was at work again last weekend, shooting a scene for a 40-year passion project whose status is almost as mysterious as its subject: the industrialist Howard Hughes.
By habit, Mr. Beatty often returns to an almost finished film to pick up some detail, even a small one — say, the image of a dog walking past a door. This time he was back, working on a picture, still untitled, that he began in 1976 and for which he is the writer, director, producer and star.
That film, so far invisible and largely shot nine months ago, may be nearing completion and could be ready for release this year.
When it finally reaches an audience, the film could crown a storied career for a wily Hollywood operator — in his prime, Mr. Beatty was nicknamed the Pro — who became known for bedding starlets, pursuing Oscars and defying the conventional wisdom with wildly unconventional pictures like “Reds” and “Bonnie and Clyde.” Or it might become a bizarre footnote to his foibles, alongside misfires like “Ishtar” and his last major acting effort, “Town & Country,” released 14 years ago.
If, in fact, this filmmaker-star, still baby-faced at 77, ever stops tinkering with a film that features stars like Lily Collins; Matthew Broderick; Martin Sheen; Mr. Beatty’s wife, Annette Bening; and Mr. Beatty himself as Hughes. Reached through his hilltop office on Tuesday — he runs his production company out of a nondescript professional building behind a strip mall near Mulholland Drive — Mr. Beatty declined to discuss his progress on the movie. As ever, it was a charming turndown.
“I would appreciate if you would say Mr. Beatty good-naturedly declined to comment,” he said.
Mr. Beatty’s project has proved almost as elusive as Hughes, who died in April 1976. But that was not before he had captured the attention of Mr. Beatty, who, a few years earlier, had observed secretive comings and goings around Hughes’s rooms at the Beverly Hills Hotel. Eleven days after Hughes’s death, the trade publication Variety reported that Mr. Beatty was at work on a biopic.
“Good luck to him!” Jane Russell, who starred in various films for Hughes, told the columnist Army Archerd. “But I won’t go see it.” (And she won’t: Ms. Russell died, at 89, in 2011.)
According to the Internet Movie Database, a widely used log of film information, the long-promised Hughes movie — or, more properly, its spiritual descendant — is finally to be released on May 21. Yet the date is inaccurate, perhaps reflecting speculative reports that Mr. Beatty would have it ready for the annual spring festival in Cannes.
People involved with the production, speaking on condition of anonymity because of confidentiality strictures, say the movie instead may be done late this year, possibly in time for the coming Oscar season. Mr. Beatty, nominated 14 times, has won once, as the director of “Reds,” in 1982.
How the new movie will be distributed is still unsettled. New Regency Pictures, which is producing it with Mr. Beatty, releases its films through 20th Century Fox or the awards-oriented Fox Searchlight unit. But people briefed on the situation said decisions about the scope, timing and precise vehicle for the film can be answered only when the movie is finally seen.
Of financial backers, Mr. Beatty has no shortage.
Though “Town & Country” was a resounding flop — it took in only about $10 million at the worldwide box office after New Line Cinema released it in 2001 — the new film, with a budget of roughly $30 million, has drawn contributions from a sluggers’ row of billionaires, savvy media executives and scions of wealthy families.
Those investors include the New York fund manager John Angelo, the Hollywood moguls Ron Burkle and Arnon Milchan and the producers Jeffrey Soros and Sarah E. Johnson, both members of affluent families with film production credits that, in Ms. Johnson’s case, include this year’s best picture, “Birdman.” Also in the lineup are Brett Ratner and the Australian billionaire James Packer, through their RatPac Entertainment company.
The various backers declined to comment or did not respond to queries.
Another backer is Terry Semel, who had reason to know this could take a while: In 1989, Mr. Semel, then a top film executive at Warner Bros., was ready to shoot a version of the Hughes film, which involved the screenwriter Bo Goldman, when Mr. Beatty, then 52, became occupied instead with a Disney film, “Dick Tracy,” in which he starred with his love du jour, Madonna.
Mr. Goldman, who wrote “Melvin and Howard,” an earlier Howard Hughes movie, said he is watching carefully to see whether anything from his own contribution to the Warner project — now owned by Mr. Beatty, according to Warner — will appear in the current film. “We weren’t sent a script, but that’s Warren,” said Mr. Goldman, who is 82.
In truth, according to one person briefed on the evolution of Mr. Beatty’s film, it has changed considerably with the years, and is no longer entirely about Howard Hughes.
Instead, this person said, it has become a somewhat lighthearted story about a young woman, played by Ms. Collins, who, like Mr. Beatty, was raised by Southern Baptists, and who — again, like Mr. Beatty — found her way to Hollywood in 1958. There, she is put under contract by Hughes, by then a film mogul. Together with another young arrival from the heartland, played by Alden Ehrenreich, she experiences the collapse of an old moral order and the rise of a new one in the early 1960s. Again, as Mr. Beatty did.
Seasoned actors populate the film. In addition to Mr. Broderick, Mr. Sheen and Ms. Bening, they include Dabney Coleman, Candice Bergen and Oliver Platt. Alec Baldwin appears in a cameo role as the Hughes associate Robert Maheu.
Much of the film was shot around Los Angeles last March and April, both in Sunset Gower Studios in Hollywood, which housed Columbia Pictures through the 1960s, and on locations, among them the downtown Millennium Biltmore Hotel, that are redolent of the Hughes — and Beatty — era.
During his years out of the limelight, Mr. Beatty has raised four children with Ms. Bening, at whose side he will occasionally appear in public, as he did last November at the Governors Awards banquet of the Academy of Motion Picture Arts and Sciences.
But, like the heiress Sarah Winchester, who never stopped working on her famous mystery house, Mr. Beatty has also been occupied with his favorite work in progress.
Last week a public relations representative said the filmmaker would happily talk when he finishes.
The author Peter Biskind recalls being told the same thing when he was completing his book “Star: How Warren Beatty Seduced America,” a biography first published in 2010.
The Hughes movie “is still not out, may not appear until next year, who knows?,” Mr. Biskind noted in an email.
“Had I listened to him, my book would still not have seen the light of day.”A version of this article appears in print on , on Page C1 of the New York edition with the headline: Shooting Can Wait. For Years.. Order Reprints | Today’s Paper | Subscribe