It’s not Washington, it’s HBO.

Starting this fall, the cable channel known for “Sex and the City” and “The Sopranos” will shift its focus to the Beltway with a 10-episode docudrama series that seeks to explore the culture and careers of Washington’s lobbyists, image-makers and power-brokers.

“K Street” will feature a fictional law firm and fictitious lobbyists — led by the bipartisan duo of James Carville and Mary Matalin — dealing with real-life Members of Congress and present-day issues. It aims to capture a no-holds-barred, real-life picture of how Washington works.

“This is a realistic view of how public policy is made,” Carville said. “There are people in Washington who are trying to make money off politics.”

Each episode will be shot with handheld cameras the week before it airs in order to make the show timely and relevant.

HBO hopes the unscripted, on-the-fly technique will offer some authenticity to the series as the directors and actors — like real-life lobbyist and firms — make spur-of-the-moment decisions about strategy and tactics.

“It’s akin to being a piano player in a whorehouse, we try to hum it and somebody will pick it up as it goes along,” said Carville, one of two of Washington insiders who came up with the idea for the show and will help to get it off the ground.

Though no decisions have been made about topics, episodes could range from campaigns to block energy legislation and approve asbestos reform to launching public relations efforts to restore the image of accused Los Angeles Laker Kobe Bryant or take down Saudi Arabia, according to those involved in the project.

Carville conceived the show earlier this year with Republican image-maker Michael Deaver, a communications strategist for former President Ronald Reagan now with Edelman Worldwide.

The two contacted Hollywood producers Steven Soderbergh (“Traffic,” “Ocean’s Eleven”) and actor George Clooney who, in turn, sold the project to HBO.

“‘K Street’ will offer a fascinating look inside a world that few people ever experience first hand,” said Carolyn Strauss, a senior executive at HBO.

HBO will air ten, largely improvised, half-hour episodes on Sundays beginning Sept. 14. The show will be shot Mondays, Tuesdays and Wednesdays, edited on Thursdays and Fridays, and will air Sunday nights.

“Monday morning, the creative group and the actors get into a room, discuss what happened over the weekend, read all the papers for the morning and decide on the spot what our show is going to be about,” Soderbergh said in mid-July when HBO previewed the show for television critics. “We shoot for two and half days, we edit for two days and we air that Sunday. So it’s being written, it’s being performed sort of spontaneously.”

Mary McCormack (“K-PAX,” “Full Frontal”), John Slattery (“Traffic,” “Ed”) and Roger Smith (“Oz,” “Summer of Sam”) will serve as the only actors in the series.

Carville, Matalin and Deaver play themselves in the show while serving as off-air consults.

In the show’s 10-minute pilot, Carville and Matalin work as lobbyists for a fictional political consulting firm hired to help secure U.S. support for installing exiled Iraqi leader Ahmad Chalabi as the head of the rebuilt Iraq.

Much of the pilot was shot in the backseat of a cab and at The Palm steakhouse, where the firm’s lobbyists plot strategy.

In another scene, shot in Edelman’s 9th-floor conference room, lobbyists learn that Chalabi has a checkered past: Years ago he was sentenced to a 22-year prison term for stealing $250 million from a bank in Jordan.

“All we have to do is clean this guy up. We don’t have to run him,” says a lobbyist played by McCormack. “All we have to do is clean him up and make a s—load of money.”

One lobbyist takes the lead with the administration, working to persuade President Bush or Defense Secretary Donald Rumsfeld to mention Chalabi’s name in public.

On Capitol Hill, another lobbyist meets with Sens. Hillary Rodham Clinton (D-N.Y.), John McCain (R-Ariz.) and Orrin Hatch (R-Utah) to build support for Chalabi.

In a brief encounter in a hallway in the Russell Senate Office Building, McCain cautions McCormick: “Your reputation is such that you want to be careful” representing Chalabi. However, McCain added: “People have represented Liberia in this town.”

In her meeting with Hatch, McCormick slyly mentions that she is a Republican. “Good,” Hatch responds, before adding judiciously: “You didn’t have to be to get in here, but I recognize your firm, and I think you do a really good job.”

Critics of the show say it could confuse viewers about what is fiction and what is reality.

Chalabi, for example, never stole money from Jordan and has not hired a Washington firm to work on his behalf.

“It’s faction,” Carville said, “some fact, some fiction.” Soderbergh dubs it “real-time fiction.”

“K Street” will have some legal protection because politicians are public figures, the show’s producers say.

“If you’re a public figure, period, and you’re taking a public stance, then all bets are off,” Clooney told the television critics last month.

Still, HBO expects complaints.

“People have to remember, it is a television show, any attempt to make it into anything else is wrong,” Carville said. “I’m sure there will be a thousand complaints. But people complain about everything. Hopefully, as they complain, they will be entertained.”

Carville’s warning is appropriate for a cable channel whose motto is: “It’s not television, it’s HBO.”