By Steve Gorman

LOS ANGELES (Reuters) - U.S. television's top show, "American Idol," returns to the Fox network on Tuesday, poised to stand taller than ever in the ratings as it arrives in a prime-time landscape clouded by the Hollywood writers strike.

Anticipating another blockbuster season for the TV talent competition, advertisers already have ponied up banner prices for the seventh round of "Idol," making it again the most lucrative regularly scheduled series in prime time.

The show, generally airing twice weekly, averaged over 30 million viewers per episode last season.

Months before the writers strike began on Nov. 5, a 30-second commercial for the 2008 season of "Idol" was going for roughly $750,000. The price jumped to at least $900,000 for the same ad just before the show's return, according to media buyers familiar with the deals.

Both figures are up sharply from ad rates fetched for last year's show, which features amateur singers from around the United States competing for fame and a recording contract.

The advertising value of "American Idol," the most watched U.S. series for the past four years, has only been enhanced by the ratings declines faced by Fox's network rivals in a environment weakened by the writers strike.

Even before the Writers Guild of America launched its walkout against film and TV studios, prime-time ratings for the major networks across the board were down about 10 percent from the same period in 2006.

"If you have a show that you know is going to deliver like 'American Idol,' that's going to jack the prices up," said Brad Adgate, research director at New York-based Horizon Media.

SURE-FIRE RATINGS

The strike, now in its 11th week with no settlement in sight, has halted production on prime-time dramas and sitcoms. Except for a handful of series the networks were holding back for a mid-season launch this winter, the supply of fresh episodes for most scripted shows is about to run dry.

As a result, broadcasters are starting to fill schedules with a heavy dose of reality TV and game shows -- programs immune from the writers strike and cheaper to produce but generally less popular with viewers.

That makes a sure-fire ratings winner like "American Idol" all the more attractive to advertisers, and amplifies its importance as a promotional platform for other Fox shows.

In fact, Fox scored a ratings success this past Sunday with the launch of its sci-fi action drama, "Terminator: The Sarah Connor Chronicles," which was heavily promoted with "Idol."

Powered in large part by "Idol's" success last year, Fox finished the 2006-07 TV season as the top-rated network among viewers aged 18 to 49, the young-adult crowd most prized by advertisers. Still, it appeared that by last season's May finale "Idol" may have hit its peak.

For the sixth season as a whole, the show was down slightly in overall audience compared with 2006, and off a bit more in its 18-49 ratings. That marked the first year-to-year decline in the show's Nielsen numbers since its 2002 inception.

But "Idol" remained a cash cow for News Corp.-owned network with undiminished advertising revenues.

"Idol" last season generated $810 million in advertising revenues, up 39 percent from the year before, according to figures from industry tracking service TNS Media Intelligence cited by the Los Angeles Times.

(Additional reporting by Paul Thomasch)