NEW YORK — Fox executives promised to boost a sagging “American Idol” as they confidently outlined plans on Monday for a new season and declared the network the one that “delivers America’s favorite shows.”

Fox is making a special effort to establish new comedies next season, introducing shows that feature Keri Russell and Cloris Leachman. Its big-ticket drama is a fantasy adventure series from Steven Spielberg, although executives conceded there’s a chance it won’t be ready next season.

Fox will finish the 2009-10 TV season as the second most popular network behind CBS but first among the 18-to-49-year-old audience it targets for a record sixth straight year. Its executives told advertisers on Monday that they won’t see a richer, more diverse array of programming from another network during this week of schedule announcements.

“Fox delivers America’s favorite shows,” said Peter Rice, entertainment chairman of the Fox Networks Group.

Still, its most compelling mystery for next season remains: Who will replace Simon Cowell when he leaves “American Idol” this month?

That search is top priority for Fox this summer, Rice said

“We have to find a judge to replace Simon who provides both musical credibility and an incredible entertainment value,” he said. “Anytime you have a change, it’s something you have to do right.”

While it’s still television’s favorite show, “American Idol” has seen its ratings drop by 8 percent this season, according to the Nielsen Co. In response to viewer requests for more performances, Fox will increase the Tuesday night competition show from an hour to 90 minutes. The Wednesday results show will be chopped in half to 30 minutes.

Fox is giving extra attention to “Glee” in its second season, even though fans will get a scheduling challenge. A special episode of the show will get the prime post-Super Bowl time slot next season.

“Glee” will air at 8 p.m. Tuesdays in the fall, ahead of two new comedies. After the Super Bowl, it will switch to 9 p.m. Wednesdays, following the “American Idol” results show.

The first new Tuesday comedy is “Raising Hope,” about a 23-year pool cleaner who suddenly has to raise his baby. Sitcom veteran Leachman appears in the character’s family.

“Running Wilde” has star power, with Will Arnett portraying a playboy trying to woo his high school sweetheart, played by Russell.

Spielberg’s “Terra Nova” is an epic that follows a family from 2149 as it goes back to prehistoric times trying to save the Earth. It hasn’t been given a slot on the schedule yet, however.

“What we want to do is commit to do it right,” said Kevin Reilly, Fox network entertainment president.

Besides the two comedies, the only other new series Fox is introducing in the fall is “Lonestar,” a prime time soap about a Texas family with feet in both the working class and high finance worlds.

On four of the seven nights, Fox’s prime time schedule this fall will be the same as it is this season.

Fox series that will appear later in the year are:

—”Bob’s Burgers,” an animated series about a family-run business and its cutthroat competition with “Jimmy Pesto’s Pizzeria.”

—”Mixed Signals,” a comedy about three friends trying to balance relationships with a need for freedom.

—”Ride-Along,” a cop series set in Chicago that tries to give viewers the sensation that they’re spending a shift in a squad car.

Online:

www.fox.com/