By Ian Simpson

WASHINGTON (Reuters) - U.S. journalist Gwen Ifill, who co-anchored "The PBS NewsHour," wrote a best-seller about President Barack Obama and moderated two vice presidential election debates, died on Monday, the public broadcaster said. She was 61.

Ifill died surrounded by family and friends after several months of treatment for cancer, PBS said in a statement. The network said on Nov. 2 that she would be off the air as she dealt with unspecified health problems.

"Gwen was a standard bearer for courage, fairness and integrity in an industry going through seismic change," said Sara Just, PBS NewsHour executive producer.

She called Ifill "a journalist's journalist" who combined warmth and authority so well that people on the street who had seen her on television would hug her.

Ifill was moderator and managing editor of "Washington Week," a prime-time news program, and co-anchor and managing editor for "The PBS NewsHour" with Judy Woodruff.

Ifill joined the programs in 1999 from NBC News, where she was chief congressional and political correspondent, according to a biography on the "NewsHour" website.

She also had been White House correspondent for the New York Times and a reporter for the Washington Post, Baltimore Evening Sun and the Boston Herald American.

On the "NewsHour website, Ifill said that "public broadcasting provides the best of both worlds - combining the depth of newspapering with the immediate impact of broadcast television."

Ifill was the best-selling author of 2009's "The Breakthrough: Politics and Race in the Age of Obama" and moderated the vice presidential debates during the 2004 and 2008 national elections.

She covered seven presidential campaigns and won the George Foster Peabody Award in 2008 for bringing "Washington Week" to live audiences around the country.

A native of New York and a graduate of Boston's Simmons College, Ifill received more than 20 honorary doctorates. She was included in Ebony Magazine's list of 150 Most Influential African Americans.

In a bipartisan reaction, Republican House of Representatives Speaker Paul Ryan and Obama, a Democrat, expressed sorrow about Ifill's death. On Twitter, Ryan called her "an incredibly talented and respected journalist."

"I always appreciated Gwen's reporting, even when I was at the receiving end of one of her tough and thorough interviews," Obama said at a White House news conference.

(Reporting by Ian Simpson; Editing by Dan Grebler, Bernard Orr)