The NBC Hit Machine Loses Its Momentum : Television: CBS takes the first week from the five-year ratings leader. No new series on any network cracked the Top 10.

One week does not a TV season make, but there may well be some sweaty palms today over at ratings leader NBC.

It’s not just that national figures released Tuesday showed that NBC lost the first week of the new season to upstart CBS--which was powered by such new entries as Sharon Gless’ “The Trials of Rosie O’Neill” and the comic strip “The Flash.”

It’s not just that NBC, the ratings champion for five consecutive years, now has lost two weeks in a row.

And it’s not just that the network of “Cheers” and “The Cosby Show” apparently has come back to Earth and is “vulnerable,” as Brandon Tartikoff, chairman of the NBC Entertainment Group, has pointedly said.

No--despite all that, NBC is still the favorite to win again this season under the watchful eye of its corporate owner, General Electric, unless ABC’s “Roseanne” & Co. lineup suddenly bursts farther upward as the prime challenger.

But what has to make NBC executives rather nervous is that the network’s nine new series that it boasted were its strongest crop in years don’t seem to have grabbed large, immediate viewer interest. What must be particularly disappointing is the mediocre tune-in thus far for “Fresh Prince of Bel Air,” the sitcom Tartikoff suggested would be the network’s biggest breakout hit since “The Golden Girls.”

It certainly isn’t thus far. It may well have shot its bolt with its outstanding pilot episode, which seemed to indicate superstardom for the star, young rapper Will Smith.

Tuesday’s ratings from the A.C. Nielsen company showed the tightest opening-week race since 1966, with only four-tenths of a point separating the Big Three.

Fox Broadcasting was a non-contender as it awaits new episodes of “The Simpsons,” and it may be paying the price for overhauling its schedule, in the process dumping such established shows as “21 Jump Street” and “Booker.”

CBS led the way in last week’s opening salvo with a 13.6 rating and 23% of the audience. NBC was second with 13.4 and also attracted 23% of viewers. And ABC was third with 13.2 and 22%. Fox pulled a 5.0 and 8%. (Each ratings point represents 931,000 homes.)

With all the special previews, program stunting--and more premieres yet to come--it would be foolish to make too many long-range judgments based solely on last week. “Premiere week almost by definition is an atypical week,” announced NBC, which, if memory serves, made no similar distinction in the past when it won.

NBC’s headache is as clear as the ratings for last week. Its highest-ranked new series, the Robert Urich sitcom “American Dreamer,” came in 20th, but only because it was previewed following the No. 1-rated “Cheers” and out of its regular time slot. Here’s how NBC’s other new series fared:

“Fresh Prince of Bel Air” ranked only 41st among 89 shows. “The Fanelli Boys” was 51st. “American Dreamer,” in its regular time period, came in 53rd. “Law and Order” was 54th, “Ferris Bueller” 57th, “Working It Out” 58th and “Parenthood” 67th.

NBC points out that its two other new series, the medical anthology “Lifestories” and the musical “Hull High,” were not shown last week. But they were broadcast previously, and they seem to have little chance of becoming major ratings contenders.

CBS may have benefited to some degree from the network’s promotional tie-in with the K mart retail chain. NBC’s similar promotional tie-in with McDonald’s, just gearing up, could also have an impact. But it didn’t Monday night, as ratings launching the second week of the season indicated so-so statistics again for “Fresh Prince” and “Ferris Bueller.”

Bottom-ranked CBS was exultant over last week’s results. It was the first time that the network has won a premiere week since 1984. And it was the first time CBS has won a week outright during the season since 1987. No matter how you look at it, last week was a terrific morale builder for CBS under its new entertainment division president, Jeff Sagansky.

CBS’ new Tuesday motion-picture package made a major impact last week as “Field of Dreams” ranked 17th despite the competition of “Roseanne,” which still finished No. 2, but was 22% off from its 1989 premiere.

Gless, as a public defender in CBS’ “The Trials of Rosie O’Neill,” was 28th. “The Flash,” the underdog in head-on competition with “The Cosby Show” and “The Simpsons,” came in 34th with a surprisingly solid 23% audience share. And another new CBS series, “Uncle Buck,” was right behind at No. 35, taking the measure of “Fresh Prince of Bel Air,” its own head-on competitor.

Yet another new CBS series, the Burt Reynolds sitcom “Evening Shade,” pulled a respectable 24% share in 45th place.

ABC sportingly noted that NBC’s ratings were 20% lower than premiere week a year ago. However, no new series on any network cracked the Top 10 shows.

For CBS, the best news is that if its new series show any staying power, the network may finally be on its way to solving its toughest problem--getting 8 p.m. hits that hook viewers for a night. Early results show possibilities for CBS on five nights: “Uncle Buck” on Monday, “Rescue 911” on Tuesday, “The Flash” on Thursday (still a long shot), “Evening Shade” on Friday and “Murder, She Wrote” on Sunday.