(Reuters) - Pulitzer Prize-winning U.S. film critic Roger Ebert says he is battling cancer again and that he will scale back his writing by taking a "leave of presence" from his more than four-decade career.

Ebert, 70, known for his rhetorical power and prolific output, said he will undergo radiation treatment that will force him to take time away from his job.

"I must slow down now, which is why I'm taking what I like to call 'a leave of presence,'" Ebert said in a blog entry posted late on Tuesday, adding that he would scale back his workload.

Ebert, who had lost his ability to speak and eat after surgeries for thyroid and salivary gland cancer in 2002 and 2003, said the cancer was discovered by doctors after he fractured his hip in December.

"The 'painful fracture' that made it difficult for me to walk has recently been revealed to be a cancer," Ebert said, giving no further details about the type of cancer or diagnosis.

"I am not going away," Ebert said. "My intent is to continue to write selected reviews ... What's more, I'll be able at last to do what I've always fantasized about doing: reviewing only the movies I want to review."

The Chicago resident said he also would take time to write about his illness.

Ebert, whose reviews are syndicated to more than 200 newspapers, has been reviewing films for the Chicago Sun-Times since 1967. He won the Pulitzer Prize for criticism in 1975.

He gained national prominence with the late Gene Siskel on the television show "At the Movies with Gene Siskel and Roger Ebert," coining the phrase "Two Thumbs Up," until Siskel's death in 1999. He later teamed with critic Richard Roeper but quit for health reasons.

Forbes dubbed Ebert the most powerful pundit in America in 2007. 

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