Rachel McAdams streaks across Morning Glory, a diverting comedy about the three-ring circus of morning programs, like dimples shot from a cannon. She's sharp, sexy and funny. Too bad the script does not permit her to be all three at the same time.

After Becky Fuller (McAdams) is fired as assistant producer of "Good Morning, New Jersey," she gets hired as producer/ringmaster of "Daybreak," a morning show with ratings in the cellar and staff morale in the sub-basement.

Can Becky revive the moribund show? Can the gal who rises at 3:30 am and is all in by 7 pm find romance? Can this cookie forge a workplace alliance with crusty Mike Pomeroy (Harrison Ford) a newsman old enough to be her father?

The script from Aline Brosh McKenna (screenwriter of The Devil Wears Prada) juggles the balls of workplace comedy, job-versus-love conflict and displaced daddy/daughter romance. In the hands of director Roger Michell (Notting Hill), they do not stay up in the air, but drop, thud, dribble.

When Becky fires the sleazy foot fetishist who is one of Daybreak's co-anchors, she is left with Colleen (Diane Keaton), who chirpily predicts that the newbie will fail, "like everyone before you."

To give the show some tough to complement Colleen's fluff, Becky taps Mike, a hard-news legend running out the clock on his contract.

You would think that with two deft Hollywood veterans at his disposal, Michell would let Keaton do her airy and Ford his wary thing. You would be wrong. Unaccountably, Keaton is underutilizeed, if funny. A subplot involving Becky and TV executive played by Patrick Wilson, scored to adult-alternative rock, likewise goes nowhere.

What Morning Glory has going for it is McAdams, who has the motormouth delivery ideal for comedy and who nails the micromanager mentality of kindred McKenna heroines in Prada and 27 Dresses. These are women who are lovely, could run empires and, we are led to believe, have trouble getting dates.

An antecedent of this type of Type A female professional is the Holly Hunter character in Broadcast News. But though their milieus and personal problems are similar, Becky couldn't be further from News' Jane Craig. Jane sets the bar high and fights to keep the news fluff-free.

What a difference 20-odd years makes: Becky's all about lowering the bar and chasing those ratings. (Some of the funniest involve the weatherman, nicely played by Mtt Malloy). When Mike complains that doing soft-news segments would dull his hard-news edge, Becky snaps: "That battle is over. You lost."

In rhythm, humor and performance, Morning Glory is, at best, sporadic.