In a Oct. 2, 2009 pool file photo, Robert J. Halderman appears in State Supreme Court in New York. (THE ASSOCIATED PRESS/Marc A. Hermann, Pool, File)

NEW YORK - David Letterman was on the receiving end of a sales pitch, not a shakedown, a defence lawyer said Tuesday as he argued that a TV producer accused of extorting the comic was simply peddling a screenplay.

Robert J. (Joe) Halderman's lawyer asked a judge to toss the attempted first-degree grand larceny case, which spurred Letterman to acknowledge his office dalliances in a startling on-air monologue last month. Attorney Gerald Shargel said the $2-million exchange was business, not blackmail.

"There was a commercial transaction. Nothing more," he said.

The first outlines of Halderman's defence spotlighted Letterman's behaviour, drawing a sharp response from the "Late Show" host's camp. A lawyer for Letterman said the comic was prepared to testify if the case went to trial.

"It's classic blackmail, no matter how Mr. Halderman's lawyer wants to dress it up," Letterman attorney Daniel J. Horwitz said outside court.

In papers filed Tuesday, Shargel argued that the indictment against Halderman should be dismissed because his conduct wasn't a crime, among other claims. Assistant District Attorney Judy Salwen said she was confident a judge would find the indictment was on solid legal ground.

State Supreme Court Justice Charles Solomon is expected to rule in January.

Halderman acknowledges slipping Letterman's driver a package on Sept. 9 that included the supposed screenplay "treatment" - or synopsis - and some "source material."

Authorities say the materials included a letter saying Halderman needed to make "a large chunk of money" and a claim that the screenplay would depict how Letterman's world would "collapse around him" when information about his private life was disclosed. Photos, personal correspondence and portions of a diary also were enclosed, authorities said.

The diary entries were allegedly written by Halderman's former girlfriend and outlined her affair with Letterman.

Authorities then taped two conversations between Letterman's lawyer and Halderman - including an exchange in which the lawyer gave Halderman a phoney $2-million check after he demanded it as hush money, the Manhattan district attorney's office said. Halderman was arrested after depositing it.

The day before prosecutors unveiled the case last month, Letterman divulged it on his show, acknowledging he had had sex with women who worked for him.

Shargel's court filing said Halderman simply realized he had "a valuable subject for a book or a movie" and sold it to Letterman, threatening to do nothing more than sell it elsewhere if the TV host rejected it.

"I have no plans to do anything other than either sell you this option - this screenplay - to you and therefore you own the story. Or if you don't and you're not interested, as I've said, then that's fine, and I will proceed, and I will do what I want to do, which is what I've been thinking about doing, anyway - which is writing a book," Halderman told Letterman's lawyer in one of the taped exchanges, according to the filing.

Letterman's lawyer said criminal charges would follow if Halderman released the information himself, the filing said. Halderman, it said, responded: "I don't agree with your position on that."

Some other defendants in extortion cases have argued they were just doing business. In the 1980s, a Maryland union official accused of demanding cash to approve payments to a building contractor maintained the two had a business dispute over construction costs for the union headquarters; the union official eventually pleaded guilty.

Legal experts say the line between extortion and playing hardball can be blurry.

"A lot of blackmail and hush-money cases play right at the edge of legitimate transactions," said Pace Law School professor David N. Dorfman.

But Letterman's lawyer said Halderman's tactics - such as delivering his message to the comic's car around 6 a.m. and demanding a response within two hours - blunt any claim that his aims were purely commercial.

Halderman had changed the characters' names but envisioned a behind-the-scenes tale of the "atmosphere and conduct" of Letterman and the "Late Show," his court filing said.

It said Halderman had evidence that "Letterman had created and fostered an environment of workplace sexual misconduct" that amounted to sexual harassment - a question that has become an issue since the comic's disclosure of his office affairs.

The president of the National Organization for Women called on CBS last month to "recognize that Letterman's behaviour creates a toxic environment." The network declined to respond publicly.

Shargel declined to describe what Halderman said he had found. The court filing noted only that Letterman himself described his conduct with female employees as "creepy."

Letterman's lawyer strove to keep the focus on the extortion case but added that no one has ever made a formal sexual harassment claim against the comic.

"His conduct's not an issue here," Horwitz said after the brief court session.

Halderman declined to comment. The 52-year-old producer for CBS' "48 Hours Mystery" has pleaded not guilty. He could face five to 15 years in prison if convicted.

CBS declined to discuss his status at the network, where he has worked for more than 27 years.