As part of the initiative, Mr. Gianopulos said, Fox will finally join the UltraViolet digital locker system that is already used by Warner Brothers, Universal Pictures and others to make films available, once purchased, on virtually any of a consumer’s entertainment devices.

Earlier this year, Jeffrey L. Bewkes, the chief executive of Time Warner, said he would not be opposed to earlier sale of Warner films on UltraViolet, as long as the studio felt antipiracy measures were working, though he stopped short of putting a program into place.

Mr. Gianopulos said it was not so much concern with piracy that had kept Fox out of UltraViolet until now as it was other early concerns with the workability of the locker system. He said he believed Fox was the first studio to go so far as to offer a three-week early window for digital sales.

“We’re trying to get this process started,” he said.

Mr. Gianopulos said Fox would offer the early, lower-priced sales on all of its forthcoming movies for an indefinite period, while monitoring the results. Based on discussions with exhibitors, Fox executives said they believed the move respected any concerns about narrowing the theatrical window. Mr. Gianopulos acknowledged that Fox was nudging home video “a little closer” to the theatrical release. But, he said, most films are out of theaters long before they will be available for purchase digitally.

According to figures from the Digital Entertainment Group, an industry consortium, digital sales of films and television shows — as opposed to revenue from rentals or on-demand viewings — rose almost 22 percent in the first six months of this year, to $329.4 million, from $270.3 million in the first half of 2011.

But digital sales remained relatively small when compared with the sale of movies and shows on discs, which totaled $3.7 billion for the first six months of this year, down about 3.6 percent from the same period last year.