Ms. Roberts is squared off against more than two dozen stars, including the governor of California, who are jammed into a pair of competing movies. Those are “The Expendables,” from Lionsgate, and “Scott Pilgrim vs. the World,” from Universal Pictures, both also set for release on Friday.

It might be coincidence. Or maybe it is a trend.

Either way, Hollywood has been serving up its leading men, leading ladies and principal supporting players in sizable clumps of late.

“Red,” an action picture from Summit Entertainment; “New Year’s Eve,” a romantic collage from New Line Cinema; and “The Avengers,” which collects superheroes from Marvel, are examples of group enterprises on tap for the future. Sony’s “Grown Ups” and New Line’s “Valentine’s Day” showed the power of ensemble in months past.

In recent years series like “Twilight” and “Harry Potter” have been thick with cast and characters, in sharp contrast to the lone wolves and duos who carried films like “Die Hard”and “Lethal Weapon.”

For Robert J. Thompson, the founding director of the Bleier Center for Television and Popular Culture at Syracuse University, the multiplicity is no accident.

“There’s a much larger thing going on here,” Mr. Thompson said. He theorizes that feature film is reaching toward the complex, multicharacter scenarios that have made hits of sophisticated television series like “Mad Men” and “The Sopranos.”

Others are less sure.

“I don’t know that anything is changing” in terms of storytelling patterns, said Marc Platt, a producer of the cast-heavy “Scott Pilgrim.”

That film, he noted, just happened to be based on a comic book story that required Pilgrim to defeat his girlfriend’s seven “evil exes.” So seven villains the movie got, led by Jason Schwartzman (“Funny People”). The line on the bus posters: “So many bad guys. So little time.”

Even so, Mr. Platt said in a telephone interview, falling star salaries and a declining number of films have made it easier to round up an ensemble. “A lot of actors want to go to work,” he said.

That was apparent at the Comic-Con International pop culture convention last month in San Diego, where Edgar Wright, the director of “Scott Pilgrim,” introduced a panel that included no fewer than 13 cast members, among them Mr. Schwartzman and Anna Kendrick (“Up in the Air”). Michael Cera, who plays the hero Scott Pilgrim, wore an overstuffed Captain America suit onstage, presumably so fans could pick him out.

At a panel earlier that same day Sylvester Stallone, who directed “The Expendables,” had only about half of his outsize cast in tow. Eric Roberts, Jet Li and the California governor,Arnold Schwarzenegger, didn’t show, but those on hand included Dolph Lundgren (“Rocky IV”), Terry Crews (“Terminator Salvation”) and Bruce Willis.

Mr. Willis had already introduced “Red,” a spy romp with so many actors he appeared to lose count.

“I think over 75 movie stars are in ‘Red,’ ” said Mr. Willis, who was flanked by his “Red” co-stars Helen Mirren, Mary-Louise Parker and Karl Urban. They carried the flag for an ensemble that also includes Morgan Freeman, John Malkovich, Richard Dreyfuss andErnest Borgnine.

Group film has had a long, rich history in Hollywood, from cast-laden classics like “Dinner at Eight” and “The Women” in the 1930s to star-filled disaster flicks like “The Poseidon Adventure” and “Earthquake” in the 1970s to the complicated roundelays of Robert Altman.

In 2006 Mr. Altman’s last film, “A Prairie Home Companion,” featured Meryl Streep, Lily Tomlin, Woody Harrelson, Garrison Keillor, Lindsay Lohan, John C. Reilly, Tommy Lee Jones, Virginia Madsen and Kevin Kline, among others.

But large-cast films could seem slightly suspect in a culture that honored solitary heroes like Gary Cooper (“High Noon”) and Steve McQueen (“Bullitt”) in stories that put them at odds with the world.

“I don’t think the ensemble film has ever quite taken root in America,” the film historianDavid Thomson said by e-mail this week. “It goes too much against the grain of stardom and stories about ‘important’ people.”

If that is changing, said Mr. Thompson of the Syracuse center, the shift may have something to do with an increasing willingness by film studios to play demographic games that were once reserved for television.

“It gives you a palette with a lot more color,” he said, pointing out that a large cast allows marketers to add appeal across ethnic and generational lines — though sometimes at the expense of a story’s integrity. “In some cases they’re borrowing the aesthetic of ‘The Love Boat,’ ” he said.

Occasionally, Mr. Platt suggested, the sheer size of a cast, as with the “Ocean’s 11” films, may help create brand value in projects that are reaching for any way to distinguish themselves in a crowded entertainment market.

“It may not be that ‘The Expendables’ itself is a brand,” Mr. Platt said. But as the stars pile up, he said, “they might add up, in a certain way, to a brand.”

Still, the number of famous faces does not count for much if the films aren’t worth watching, as Roger Ebert, the longtime critic, observed in an e-mail exchange this week.

“Cast size,” Mr. Ebert wrote, “has nothing to do with whether a picture is better or worse.”