THE NEXT MOB WAR on "The Sopranos" may happen off camera.

When HBO announced last August that the television show would finish with a 20-episode run that would be broken up over the next two years, it was careful to characterize it as a single season. But the concept of a "season," once quite formal, continues to get fuzzier as TV changes, and HBO's own idiosyncratic scheduling practices are part of the trend.

Now, as Time Warner Inc.'s HBO is wrapping production on the first 12 episodes, key supporting-cast members are arguing that the additional eight shows constitute a new season, and they want their contracts renegotiated, people close to the situation said.

James Gandolfini, who stars as Tony Soprano, has recently signed a new deal taking him through next year's final eight shows that pays him in the neighborhood of $1 million an episode, people familiar with his contract said. Edie Falco, who plays his wife, Carmela, also just signed a new deal for the last eight episodes, and Lorraine Bracco, who plays Tony's shrink, Dr. Melfi, is negotiating a new pact, these people say.

However, representatives for key supporting-cast members, including Michael Imperioli, who plays Tony Soprano's hothead nephew Christopher, also want their contracts to be renegotiated, people close to the situation said. Tony Sirico, who plays Paulie Walnuts; Steven Van Zandt, cast as the mob family's consigliere; and Steven R. Schirripa, whose character is Bobby "Bacala" Baccalieri, are among the other actors seeking new deals. Representatives for the cast members either declined comment or referred calls to HBO.

Historically, broadcast-television contracts covered a minimum of episodes, which could be increased if a show ran to its full complement of 22 episodes in one season. These contracts generally were based on a single 12-month period, during which many episodes could easily be produced.

HBO has its own calendar. "The Sopranos" takes long breaks and hadn't been on the air for two years until last Sunday. The show also has a remarkably long shooting schedule -- 20 days an episode -- while a network crime drama usually takes eight days. To make these 20 episodes would take much longer than one year, so they can't be called a "season," cast members argue. The show's casting demands are further complicated by its writers' tendency to rub out major characters when they see fit.

Production on the first 12 episodes could be wrapped as early as this week. With shooting for the final eight not set to start until June, HBO has time to cut new deals. For the writers of this extremely complicated show, the production demands could be more perilous. If an actor chooses to call HBO's bluff and walk off the show, it could play havoc with plot plans for future scripts.

Having to renegotiate for the last eight episodes was something HBO was trying to avoid. A spokesman for the channel said: "We're confident that everyone will be signed for the last eight episodes."

It isn't unusual for actors to try to renegotiate deals while under contract. Mr. Gandolfini has had his contract redone several times and once even filed a breach-of-contract suit against HBO, which countersued. The two sides eventually reached a new deal.

Salaries on "The Sopranos" show that Mr. Gandolfini is the Godfather in more ways than one. There is a big drop-off between his salary and that of the rest of the cast. Other major players have salaries in the low six figure range, while smaller or recurring cast members earn less than $100,000 an episode, a person familiar with the deals says. Lesser-known characters earn anywhere from $35,000 to $50,000.

Contract disputes are commonplace in Hollywood and are usually resolved before they reach a crisis. Still, changes in the ways shows are made and later sold are making even the most routine negotiations fraught with potential land mines.

Besides salaries, actors also often get a cut of the so-called back end -- money earned when a show is sold into syndication. With shows now being offered via iPods or video-on-demand and on DVDs, actors are wary about being cut out of these new revenue streams.

In the case of "The Sopranos," a crucial point could be how HBO plans to sell DVDs for the sixth season. If the cable network packages the first 12 together, and the last eight later, that would support the argument of the supporting cast that they are two separate seasons. The DVDs won't come out for months, however, so that decision hasn't been made.

Although HBO is arguing that the 20 episodes count for one season, it also recently offered some supporting-cast members a 15% bump in pay, one actor's representative said. That has emboldened those cast members who argue that they need new contracts before returning for the final eight episodes, this manager said.