The upcoming season of "The Sopranos" might well be a whopper, at least in terms of the number of episodes. Sources said series creator/executive producer David Chase is close to finalizing a pact with HBO to produce as many as 10 additional episodes for the upcoming sixth season, set to bow in March. Sources said the tentative game plan is for HBO to stretch out the mob drama's swan-song season over many months, much as it did with the final batch of "Sex and the City" episodes by running a batch of 12 from June-September 2003 and the final eight in January-February 2004. It's understood that the "Sopranos" cast and crew went into the sixth season, which recently began production on the East Coast, expecting to film at least 10 but no more than 13 episodes for Season 6. Details were sketchy late Tuesday, but sources said that Chase was close to signing on to produce at least seven more installments of the Emmy-winning series. Of course, when it comes to long-term planning for "Sopranos," the other X factor is the wishes of star James Gandolfini. It was unclear late Tuesday whether the extended-season plan would trigger new contract negotiations for Gandolfini, who set a new salary benchmark for actors toiling in the cable realm with his last contract renegotiation (HR 3/20/03). Reps for HBO and Chase declined comment on the matter Wednesday.