NBC has tapped “Saturday Night Live” exec producer Lorne Michaels to create a new series to fill the hole left by the departure of “Late Night” host David Letterman, whose move to CBS was finally confirmed yesterday at two afternoon press conferences.

NBC Entertainment prexy Warren Littlefield, meanwhile, defended his network to an overflow crowd of reporters in Santa Monica, saying there was ultimately “no way” to keep Letterman after NBC named Jay Leno host of “The Tonight Show” when Johnny Carson retired.

No concept or cast was announced for the Michaels program, which will be produced in New York by Michaels (who created “SNL,” has exec-produced 13 of its 18 seasons and will continue on that show) in association with NBC Prods.

Though Littlefield said he’d talked with Michaels as long as a year ago about a Monday-through-Friday show should Letterman pull up stakes, sources indicated as late as this week NBC was still uncertain how it would fill the “Late Night” slot.

Letterman will make his final “Late Night” appearance June 25 and will premiere on CBS in August.

The media-shy Letterman, at a New York press conference with CBS chairman Laurence Tisch and CBS/Broadcast Group prexy Howard Stringer, dismissed the idea that his comedy won’t play at an earlier hour and said his new show wouldn’t be drastically different.

Letterman underscored Littlefield’s comments by saying nothing but the 11:30 slot would have kept him at NBC and that his failure to get “Tonight” was “one of the most disappointing times in my professional life. … I don’t know of a person in comedy who didn’t grow up watching ‘The Tonight Show.’ “

NBC probably won’t introduce its new series until fall and wouldn’t say how it would fill the breach, though Littlefield wouldn’t rule out “Late Night” repeats.

He also said no consideration has been given to taking Letterman off early, suggesting a delay would only heighten anticipation for the CBS show.

The untitled hour will include most elements from the existing show. NBC has yet to decide whether it will allow the host to take features such as the Top 10 list with him, though CBS exex seem to believe finding similar alternatives wouldn’t pose much of an obstacle.

Letterman, who will receive a reported $ 14 million per year as well as rights to produce a lead-out show (which he didn’t deem a priority), said he’s leaning toward keeping the show in New York but remains undecided. It’s well-known the host and exec producer Peter Lassally, formerly of “Tonight” under Carson, would be interested in a move West, and CBS –which recently renovated its TV City production facilities–has a setting for it: the stage used for its last late night venture, “The Pat Sajak Show.”

It appears unlikely Dana Carvey will be involved in the Michaels show. Carvey wants to focus on films but has an NBC pact for TV.

The media frenzy surrounding the NBC and CBS sessions took on an almost surreal atmosphere. At NBC’s, in fact, the entertainment editor of the web’s own local station, KNBC-TV’s David Sheehan, irked reporters with loud live reports in the middle of the event.

Littlefield was initially flanked by Leno, who was helicoptered in and out to take questions prior to taping “Tonight.” Letterman also appeared on “Late Night ,” and after joking about his situation over the last several months, told viewers he’d do his last NBC show in June, adding, “Shortly thereafter we’ll be taking this program to another network–can I mention this?– taking it over there to CBS.”

“This has not been a case of somebody trying to screw somebody else,” Leno said at the press conference, maintaining that he bore no animosity toward Letterman for demanding the 11:30 slot he now occupies, nor NBC for wavering in its support, despite “Tonight’s” solid ratings.

Leno, who aided his cause in landing the show initially by courting NBC affiliates, said he had talked to nearly a third of the web’s 200-plus stations to ask their opinion about the situation.

Asked if he was bitter about NBC’s handling of the late night affair, Leno quipped, “Not for this kind of dough, please.” Though neither Littlefield nor Leno would comment, the host apparently has received a boost in salary.

Despite reports of a N.Y.-Burbank rift over the decision, Littlefield (who said he, NBC topper Robert Wright and NBC Enterprises chief John Agoglia made the final call) said the goal was to try to keep both hosts, but “one thing was consistent and one thing is clear: Dave wanted to be on at 11:30.”

When NBC named Leno host of “Tonight,” he added, the web “knew that wouldn’t be a popular decision” with Letterman but felt it had 18 months to find means to keep him, fearing at the time that Leno might jump to CBS.

Stringer, the chief architect of the Letterman negotiations with CAA’s Michael Ovitz, said the deal “was a signature for this network the likes we haven’t seen for years.”

According to Anthony Malara, CBS head of affiliate relations, there’s still confusion as to which CBS affils are locked into “The Arsenio Hall Show.” The web expects to launch Letterman with well over 90% national clearance, about 65% of that “live” and the balance on a 30-minute delay. An affiliate contractually obligated to carry something else may face Letterman on another station in the market.

Malara added that the network wouldn’t buy out station contracts with syndicators to secure an 11:30 p.m. berth. “Everybody has to make an investment, ” he said.

Letterman thanked CBS for its “generosity,” saying, “This deal certainly would have put a smile on Jack Benny’s face, even in his condition.”

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