THE acclaimed Fox series "24" has received a lot of attention over its four successful seasons: for its innovative real-time format, its braided storylines, its heady brew of national security and sentimentality, and its uncanny topicality. From Balkan nationalist revenge to rogue agents with biological weapons, wars on and of terror have been portrayed in exacting detail, shaping entertainment out of headlines that often stretch the imagination.

This is even more true of the current season. with its potent mix of diverse elements -- including a two-stage nuclear conspiracy plot; the formation of an unsympathetic confederation of sleeper cells, defense contractors and rogue scientists; and even a subplot about Sino-American conflict -- all poised for unpredictable resolution Monday evening. Yet it's possible that this year's "24" will be most remembered not for its experiments with television formulas, but for its portrayal of torture in prime time.

This is not the first time torture has been featured on the show. In Season 2, a national security adviser was interrogated with a defibrillator, while the president watched on a monitor. The Counter Terrorism Unit (C.T.U.) agent Jack Bauer extracted information from a detainee by forcing him to watch streaming video of the execution -- staged, it turned out -- of his child. Later Jack himself was captured by enemy operatives and cut, burned and shocked to the point of heart failure. Interrogation in the first three seasons involved various forms of threat and violence, meant to produce information vital to the defeat of an unending number of emergencies.

But on the present season of "24" torture has gone from being an infrequent shock bid to being a main thread of the plot. At least a half-dozen characters have undergone interrogation under conditions that meet conventional definitions of torture. The methods portrayed have varied, and include chemical injection, electric shock and old-fashioned bone-breaking. Those subjected to these treatments have constituted a broad range, too, from an uncooperative associate of the plotters to a Middle Eastern wife and son linked to an operative to the teenaged son of the current season's secretary of defense, James Heller (William Devane).