“American Idol” is doing much more than merely crowning a new pop music star. The reality series is for the second consecutive season driving the Fox network to an almost certain win for the May sweeps and to what will likely be a win for the season in the adults 18 to 49 demographic.

For the first week of May sweeps, which began Thursday, April 27, Fox was the top-rated broadcast network among adults 18 to 49, averaging a 4.5 Nielsen Media Research rating. In addition, Fox was the only network to show growth over the same week last year.

Besides easily winning Tuesday, May 2, and Wednesday, May 3, with help from “Idol,” Fox was the top network Saturday, April 29, and Monday, May 1, as well. While the music reality series in its fifth season is driving record audiences to the network, Fox’s dramas are also performing strongly, said Shari Ann Brill, VP and director of programming for Carat USA.

“They also have good support from ‘House’ doing unbelievably well, plus ‘Prison Break’ and ‘Bones,’ Ms. Brill said, adding that “24” is also firing on all cylinders. “And what’s really good is each of these dramas can sustain themselves without ‘American Idol.'”

Going into May sweeps ABC was slightly ahead for the season in the demo, with Fox and CBS following closely behind in what was basically a three-way race for the top spot. But with Fox’s twice-a-week airings of “Idol,” which is building to an increasingly competitive May 24 finale while continuing to grow its audience, “It really is Fox’s sweeps to lose at this point,” Ms. Brill said.

May sweeps also marks the last major ratings period for The WB and UPN, which are dissolving over the summer and being replaced on some stations by the new Warner Bros./CBS Corp. network The CW and on others by Fox’s MyNetworkTV programming service.

While The CW is likely to be mostly programmed with series off The WB and UPN, none of the networks’ midseason offerings are expected to make it to the fall. The WB’s dramas “Pepper Dennis” and “The Bedford Diaries” and its comedy “Modern Men” all premiered to disappointing ratings this spring, making them unlikely to get a second season on The CW for 2006-07.

In adults 18 to 49, both UPN and The WB saw double-digit declines for the first week of May sweeps compared with last year, a phenomenon that doesn’t surprise Ms. Brill, considering local stations are focused on the new broadcasting ventures coming in September.

For current WB and UPN affiliates that will be either aligned with MyNetwork or striking out as an independent in the fall, there is no incentive to promote a schedule that in four months will likely be running on a competitor, she said.

“The abandoned stations are not promoting their May programming, and what for?” Ms. Brill asked. “They are not part of the new group.”