NEW YORK (CNN/Money) - Jeff Zucker, president of NBC Universal Television Group, has to be feeling the pressure now.

NBC has long been the leader in the television industry's "upfront," the annual period when networks unveil their fall shows and sell about 80 percent of their available commercial time. Once the dominant prime time network, NBC usually signed up advertisers first and established the benchmark for ad rates.

This year, amid a steep slide in its ratings, NBC has largely been sidelined as rivals CBS, ABC and Fox brokered deals first. There have been no surprises: Viacom's CBS, according to industry insiders, was on track Friday to sell about $2.5 billion to $2.6 billion in prime time ads, a 10 percent increase from a year ago.

Reaping the benefits of an impressive comeback, Walt Disney (Research)-owned ABC saw total ad commitments surge more than 20 percent, to $2.1 billion.

Fox was flat year-over-over at roughly $1.6 billion, leading some analysts to speculate that the News Corp. (Research) unit held onto more inventory than usual in the hopes of getting higher rates closer to air-time.

By Friday it was NBC's turn at the negotiating table. Weakened by this season's 19 percent drop in ratings -- and a fall from first to fourth among 18- to 49 year-old viewers whose attention commands premium rates from advertisers -- media analysts predict that NBC could lose from $400 million to more than $600 million in ad dollars this year.

"That's a severe drop," said Jack Myers, an independent media analyst and publisher of Jack Myers Report, an industry newsletter.

It's not clear when NBC, a General Electric (Research) subsidiary, will finish its upfront sales. But given how quickly the other networks completed their deals, it's not likely to take long.

"The question now is, how far down does NBC go and how much inventory can they sell (at the rates they want)?" said Myers. He predicted the best NBC can hope for is about $2.2 billion in ad commitments, or about $500 million less than Myers estimated the network sold last year. His low number for NBC: $1.9 billion.

A Wall Street analyst agreed that NBC's rates, historically among the highest, will fall. "NBC is widely viewed as having little negotiating power in this year's market," wrote Jessica Reif Cohen in a research report Friday.

An NBC spokeswoman declined comment, citing ongoing negotiations with advertisers.

The good news so far is that ABC, CBS and Fox appear to have booked decent numbers -- an encouraging sign for an industry some say could suffer a severe ad downturn as marketers turn to the Internet, video games and other forms of entertainment to reach consumers.

"To hold steady or even be down slightly is a strong story for broadcast given all of the competition," said Myers.

Bill Carroll, the director of programming at Katz Television Group, agreed.

"It doesn't seem there's a great deal of alarm" in the industry, said Carroll, referring to this year's upfront. "The real story would be if (network ad sales) didn't grow," said Carroll.

Still, it's early yet to declare the 2005 upfront a success.

For one thing, the sales numbers coming out of the networks are preliminary; for another, the networks have a competitive interest in hyping results.

Knowing this, Myers will revise some upfront numbers down. "Historically there's been over reporting" by the networks, he said. So while the whisper number for CBS is $2.6 billion, "there are people in the (ad) buying community who think it's more like $2.4 billion."

The other key reason not to grade this year's upfront: NBC.

The network, which analysts started haggling with advertisers Thursday, needs to sign nearly $2 billion in upfront deals in order to the broadcast networks to break even this year, according to Myers' estimates.

If NBC comes below $2 billion -- either because it sells less inventory that expected and at lower rates -- the analyses will be grim. It would mark the second consecutive year in which the total broadcast network upfront was down versus the year earlier.

And if NBC finishes above $2 billion? Expect a lot of television executives to wipe their brows.

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