BURBANK, Calif. – Deep inside Stage 11 on the bustling Warner Bros. lot, a giant of a television show is starting to die.

The medical drama “ER,” one of prime time’s longest-running series, will expire next February. And “ER’s” upcoming 14th season-ender (10 p.m. EDT Thursday) will slide the show one step closer to its demise.

“It just shakes you up a little,” says executive producer Christopher Chulak on a break from directing season finale scenes on “ER’s” County General Hospital set. “One foot in the grave,” jokes “ER” special effects-meister Scott Forbes.

But “ER’s” death is more than the end of a once wildly popular TV series. It is the culmination of an era in broadcast television. Created by Michael Crichton, “ER” helped usher in a new age of top-flight TV drama in the early ’90s, along with its CBS archrival, “Chicago Hope.”

The most Emmy-nominated series ever, with 120 nods and 22 wins, “ER” launched George Clooney’s career. And it far outlasted “Hope.”

Such history permeates “ER’s” set, where Clooney’s framed basketball jersey hangs high on a wall, a memento of the mega-star’s passion for playing hoops on the studio lot.

Still, despite the scent of finality on Stage 11, executive producer John Wells isn’t getting melancholy about “ER’s” death sentence, at least not yet.

“It’s a great luxury because it means we can plan the ending properly,” says Wells, whose drama “Third Watch” was terminated more swiftly in 2005.

In a few weeks, Wells and his writing staff will hunker down to map out storylines for “ER’s” final season, which will include two new characters played by Angela Bassett and Australian actor David Lyons, and at least one return by a former star.

Although it’s unlikely Clooney will do an “ER” cameo next season, Noah Wyle has committed to four episodes as Dr. John Carter. “ER” die-hards watched Carter morph from bumbling medical student in season one to skilled physician working in the genocide zones of Africa by Wyle’s last appearance in 2006.

“Carter figures centrally in the way I wanted to end the series, which I’d planned six or seven years ago,” Wells says.

“When Tony Edwards was leaving the show at the end of season eight, I thought we would probably come to an end pretty quickly, so I spent time thinking about what the end of the series should be,” Wells recalls.

And yes, “Africa will figure prominently in the storyline of Noah’s return,” Wells says.

Wells also hints he may not be able to resist trying some nostalgic flashbacks for “ER’s” last fling.

“But we’d be concerned about doing too much in the way of fantasy sequences because of the way that ‘St. Elsewhere’ ended,” Wells says of the earlier NBC medical series. In 1988, “St. Elsewhere’s” finale implied that its entire run had been imagined by an autistic child.

Meanwhile on Stage 11, Chulak and crew are busy turning the imaginings of “ER’s” season finale script into a sequence of carefully choreographed emergency room confrontations.

Guest star Steve Buscemi, who plays a drunken patient with a dark past, wanders around looking haggard in hospital gown, frayed robe and slippers.

In the season-ender, Buscemi’s character puts the whole emergency room in danger in what Wells calls “literally a big bang” of a cliffhanger that “puts a character you love and care for in jeopardy.”

Such scenarios typically foreshadow a character’s exit from the show. But by February, “ER’s” entire cast will be gone.

“I’ll definitely cry,” says Linda Cardellini, who has played nurse Sam Taggart for five years.

“I used to love fighting with Robert Romano,” Cardellini says of the obnoxious doc played by Paul McCrane from 1997-2003. “One of my first weeks on the show we wrestled against the wall and I ripped off Romano’s artificial hand and threw it down the hall. We had fun.”

Adds Maura Tierney, “Yeah, I feel sort of unhinged, but in a good way.”

Tierney plays medical resident Abby Lockhart, a recovering alcoholic with a rocky marriage to Dr. Luka Kovac (Goran Visnjic). She will appear in only two more episodes next season, and Visnjic may not return at all, or only briefly.

“With me and Goran … we have this eight-year history, as humans and as characters. But it’s sort of time,” Tierney says of her upcoming final bow. “And it won’t be traumatic. It will be a sweet ending.”

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