HOLLYWOOD — The battle of the Davids propelled Wednesday's "American Idol" finale to one of the show's best numbers ever, with 31.7 million viewers tuning in.

Rocker David Cook's victory over the runner-up, teen crooner David Archuleta, capped a historic season for Fox, which amid the disruptions of the three-month writers' strike became America's most-watched network for the first time. It also notched its fourth straight season as No. 1 in adult viewers ages 18 to 49, according to data from Nielsen Media Research.

The 2007-08 TV season officially ended Wednesday.

The high viewership for "Idol's" Season 7 finale came as something of a surprise because the show had seen lower-than-expected ratings this season. As recently as earlier this month, "Idol" retreated to some of its softest numbers in years.

But the matchup between Cook and Archuleta evidently proved irresistible. In fact, the two-hour episode was the third-most-watched "Idol" finale, after the 2006 showdown between Taylor Hicks and Katharine McPhee (36.4 million) and the 2003 face-off between Ruben Studdard and Clay Aiken (38.1 million).

Last year's contest, between Jordin Sparks and Blake Lewis, drew 30.7 million.

The "Idol" finale was a welcome dash of good news for the broadcast TV industry, which has been brought low by the writers' strike and ongoing viewer defections to cable.

Every network except Fox saw significant ratings declines this season, including CBS, which shed 16 percent of its average total viewers compared with last season. As a result, Fox snatched the crown for most-watched network from the usual victor, CBS, with 11.1 million versus 10.5 million (these data do not include Wednesday's results).

Among the ad-friendly demographic of viewers ages 18 to 49, Fox led the season while ABC and CBS, both of which logged double-digit declines, tied for second.

Results for the May "sweeps" period, which local stations use to help set ad rates and which also ended Wednesday, were worse. Every network posted losses. NBC shed nearly one-fifth of its audience compared with a year ago.

Against that backdrop, the "Idol" numbers assume even more importance, proving that broadcast TV can still deliver huge audiences with the right program.