NEW YORK – Struggling CNN has fired Jon Klein, the head of its U.S. network.

CNN Worldwide President Jim Walton said Friday that Klein is being replaced by Ken Jautz, who currently runs HLN. The former Headline News Network has been a success in recent years with a switch to an opinionated prime-time lineup.

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Klein, a former CBS executive, has never been able to solve the puzzle of building a prime-time lineup competitive in the ratings. CNN badly trails top-ranked Fox News Channel, and MSNBC’s switch to a left-focused talk lineup at night has also left CNN behind.

The timing, however, is odd. Klein just remade CNN’s prime-time lineup with an 8 p.m. ET show starring former New York Gov. Eliot Spitzer, which debuts next week, and announced that Piers Morgan would take over Larry King’s show.

Walton also said a search is under way for a person who will serve as executive vice president and managing editor of CNN Worldwide. He said in a memo to staff members that the executive is needed to “put our multi-platform advantages more fully to work.”

Prime-time viewership is down at all the cable news networks this year, but the drop is largest at CNN. Its weekday average of 640,000 viewers is down 36 percent from 2009, and has put the network into third.

Fox is averaging 2.43 million viewers, down 5 percent. MSNBC is down 11 percent to 846,000 viewers, but that still enabled the network to pass CNN, the Nielsen Co. said. HLN is averaging 554,000 viewers, off 16 percent.