The cast of "Lost": from left, Adewale Akinnuoye-Agbaje as Mr. Eko, Jorge Garcia as Hurley, Evangeline Lilly as Kate, Naveen Andrews as Sayid, Josh Holloway as Sawyer, Matthew Fox as Jack, Yunjin Kim as Sun, Dominic Monaghan as Charlie, Daniel Dae Kim as Jin, Emilie de Ravin as Claire, Terry OQuinn as Locke, Henry Ian Cusick as Desmond and Michael Emerson as Ben. In a highly unusual move, ABC announced plans today to end the show in 2010 after three more shortened seasons of 16 episodes each. AP file photo/ABC

In a highly unusual move, the network announced plans today to end the show after three more shortened seasons of 16 episodes each.

The episodes will air consecutively, repeat-free, from February to May.

ABC's bold step marks a response to the show's producers, who have been eager to set a finish line to better plot out their convoluted mystery of plane-crash survivors and to placate fans who are frustrated that the show seemed to be vamping its way to a conclusion.

"Among fans there was an unease that they were making an investment in a show that's complicated without any sense of where that's going to lead them," co-creator Damon Lindelof said in an exclusive interview. "From the very beginning, fans and even critics have been saying, 'Are you making it up as you go along?' " which was "a legitimate question."

Now, with a still far-away ending in sight, Lindelof says he and executive producer Carlton Cuse have "specific designs for ending the next two seasons" and promises that with the answer-filled season finale May 23, viewers "will begin to get an idea of what that design will be, and it will not be at all what they expect."

The finale completed filming in Hawai'i on Saturday, a day after Lindelof and Cuse signed new contracts that will keep them working on "Lost" exclusively for the duration. With 48 more episodes due, the show will have completed 60 percent of its planned six-season run.

"It's practically unprecedented in network TV to announce the end of a show this far out," Cuse says.

ABC Entertainment president Steve McPherson says the unusual long-term commitment is "a unique situation" he would be unlikely to repeat for other series. "It's one of the best shows that's ever been on," he says. "It's got brilliant storytelling, incredible character work, and takes chances beyond anything that's on the air now."

With "Desperate Housewives," "Lost" re-energized ABC in fall 2004 and became a top 10 series. But after two time-slot switches, interruptions for low-rated repeats and a mystery that tried the patience of some fans, "Lost" has lost some steam. Ratings are down about 14 percent this season, though "Lost" still ranks highly among young adults and is the most heavily recorded show on DVRs.

McPherson concedes that splitting the current third season in two "was not the best for the show" and says the network also is discussing a return to an earlier time slot to draw more family viewership.

Shorter seasons will allow plots to be more tightly constructed and "will make it a real event," Lindelof says. "We won't have to do episodes where people are standing on the beach looking at the water and wondering what's going to happen next."

Will "Lost" risk losing fans' interest with an eight-month lag? "People wait longer than eight months for the next books and films in the Harry Potter story and they don't seem to lose interest," Cuse says. "We have faith that our audience, knowing exactly how much of the story we have left, is going to be with us for the rest of the ride."

But, Lindelof says, "the last five minutes of (this month's) finale are going to seal our fate."