By Steve Gorman

LOS ANGELES (Reuters) - U.S. television's top show, "American Idol," returned to prime time with 33.4 million viewers, down sharply from last year's record season debut but still more watched than the four other major networks combined, according to ratings on Wednesday.

The two-hour Fox network broadcast on Tuesday averaged 4 million fewer viewers overall than last season's premiere episode and fell by 13 percent in ratings for adults aged 18 to 49, the audience most prized by advertisers, Nielsen Media Research reported.

Those tallies represent a four-year low for a season premiere of "Idol," the smash hit talent contest in which amateur singers, both tone deaf and gifted, compete for instant fame and their first major-label recording contract.

Last year, "Idol" opened its sixth edition with a record 37.4 million viewers tuning in but finished the season down slightly in the ratings compared with 2006, prompting many observers to say the show's popularity may have peaked.

Increasing use of digital video recorders by Americans who prefer to record their favorite shows and watch them later also is taking a toll on same-day ratings.

But industry watchers expected "Idol" to bounce back bigger than ever this season as it returned for a seventh round in a prime-time landscape clouded by the Hollywood writers strike.

TV ratings were down 10 percent this season across the board, even before the strike began. And viewership is likely to slip lower this winter as prime time is swept by a glut of reruns, reality TV and game shows -- programs that generally draw smaller audiences than original scripted dramas and sitcoms.

Nevertheless, "Idol" remains the biggest series on U.S. television by far, and a major cash cow for Fox as advertisers clamor for an ever-shrinking assortment of big-event programs.

Months before the writers strike began, a 30-second commercial for the 2008 season of "Idol" was going for roughly $750,000, with the price jumping to at least $900,000 for the same ad sold just before the premiere date.

The next highest-rated shows on Tuesday night were NBC's "Law & Order: Special Victims Unit" and the CBS miniseries "Comanche Moon," both drawing over 12 million viewers overall.

By comparison, "American Idol" exceeded the viewership of the four other major networks combined -- ABC, CBS, NBC and the CW -- by 12 percent, Nielsen said.

(Reporting by Steve Gorman; Editing by Dan Whitcomb and Cynthia Osterman)
© Copyright 2007 Reuters.