NBC Playing Catch-Up in Prime-Time Ratings Game : Television: Network executive all but concedes crown to CBS . . . but wait until next year.

After six years as the prime-time ratings champion, NBC is all but conceding the crown to CBS this season.

Warren Littlefield, president of NBC Entertainment, said that the consistent performance of the network’s weekly series has helped it close the gap that CBS had opened at the beginning of the season. CBS led NBC by 2.2 ratings points after the World Series in October but now leads by less than a point. But with the Super Bowl and the Winter Olympics still to come on CBS, he said that he does not expect NBC to catch CBS.

“I think it would take a tremendous, tremendous score to overtake CBS this season,” Littlefield told a gathering of TV critics in Marina del Rey Thursday. “But we’re in a great position to do so next season.”

Calling NBC’s weekly entertainment programs “building blocks for the future,” and saying that they have helped stop the “ratings free-fall” that NBC has been in for three years, Littlefield announced the addition of two midseason series: “Nightmare Cafe,” a dramatic anthology series from feature film horror-meister Wes Craven about a supernatural cafe and its staff, will premiere Feb. 28 and air Fridays at 10 p.m.; and “The Powers That Be,” a comedy from Norman Lear starring John Forsythe as a Senator in pursuit of the presidency who must contend with an illegitimate daughter, will premiere in early March and air Saturdays at 8:30 p.m.

Littlefield also confirmed that this is the last season of “The Cosby Show,” the lynchpin of NBC’s powerful Thursday night lineup. Bill Cosby will leave NBC a legacy, however, in the form of a series deal with Raven-Symone (who plays the youngster Olivia) and, possibly, Malcolm-Jamal Warner (who plays Theo).

NBC also is negotiating with Paramount to get its No. 1 show, “Cheers,” back for an 11th season, he said.

In discussing his competition, Littlefield said that CBS is having problems establishing a solid schedule of weekly programs. CBS has scored in the ratings this season, he said, because of costly investments in sports packages for baseball and the Winter Olympics, forcing the network to take a $400 million write-off last year.

When asked if being unseated by CBS this season was important to NBC, Littlefield said: “That depends on what you think is important. If you want to be No. 1 with a half-a-billion dollars in major sports franchises, we could be No. 1. What we’re saying is, what about next year?”

Other program announcements from NBC:

* On Tuesday, “In the Heat of the Night,” currently airing at 9 p.m., will move to 8 p.m. “I’ll Fly Away,” currently seen there, will move to Fridays at 9 p.m. on Feb. 28, behind a run of nine original “Matlock” episodes.

* NBC has made its first series pick-up for next season, renewing the cop drama “Law & Order.” Littlefield said producer Dick Wolf deserved that because, starting Tuesday, the series will move from 10 p.m. to 9 p.m., opposite ABC’s high-rated “Roseanne.”

* Beginning Feb. 4, “Reasonable Doubts,” now on Fridays at 10 p.m., will move to Tuesdays at 10 p.m.

* For his final four weeks on “The Tonight Show,” beginning April 27, Johnny Carson will host four nights of original episodes each week, instead of three. Jay Leno takes over the show on May 25.

* A 10th-anniversary “Late Night With David Letterman” special will kick off the February sweeps in prime time Feb. 6 from Radio City Music Hall. NBC is seeking a long-term contract extension with Letterman, whose current deal extends through April, 1993.

Meanwhile, Littlefield and other senior NBC executives called upon Hollywood’s production industry to re-examine the economic structure of high-priced television contracts and production schedules to keep network television healthy in a recessive economy.

Littlefield was scheduled to meet Friday with studio heads and producers to discuss ways to cut costs without cutting production value.