WASHINGTON (AP) – Tim Russert, who pointedly but politely questioned hundreds of the powerful and influential as moderator of NBC’s ”Meet the Press,” died suddenly Friday while preparing for his weekly broadcast. The network’s Washington bureau chief was 58.

In addition to his weekly program, Russert appeared on the network’s other news shows, was moderator for numerous political debates and wrote two best-selling books.

President Bush, informed of Russert’s death while at dinner in Paris, swiftly issued a statement of condolence that praised the NBC newsman as ”an institution in both news and politics for more than two decades. Tim was a tough and hardworking newsman. He was always well-informed and thorough in his interviews. And he was as gregarious off the set as he was prepared on it.”

NBC interrupted its regular programming with news of Russert’s death and continued for several hours of coverage without commercial break. Familiar faces such as Tom Brokaw, Andrea Mitchell and Brian Williams took turns mourning his loss.

Williams called him ”aggressively unfancy.”

”Our hearts are broken,” said Mitchell, who appeared emotional at times as she recalled her longtime colleague.

Competitors and friends jumped in with superlative praise and sad recognition of the loss of a key voice during a historic presidential election year.

Bob Schieffer, Russert’s competitor on CBS’ ”Face the Nation,” said the two men delighted in scooping each other.

”When you slipped one past ol’ Russert,” he said. ”You felt as though you had hit a home run off the best pitcher in the league. I just loved Tim and I will miss him more than I can say.”

The cause of death was not immediately clear. The network said on its Web site that Russert died of a heart attack, but Michael A. Newman, Russert’s internist, later said that resuscitation was begun immediately and continued at Sibley Memorial Hospital, to no avail. An autopsy was pending, Newman said.

Russert, of Buffalo, N.Y., took the helm of the Sunday news show in December 1991 and turned it into the nation’s most widely watched program of its type. His signature trait there was an unrelenting style of questioning that made some politicians reluctant to appear, yet confident that they could claim extra credibility if they survived his grilling intact.

He was also a senior vice president at NBC, and this year, Time Magazine named him one of the 100 most influential people in the world.

Russert had Buffalo’s blue-collar roots, a Jesuit education, a law degree and a Democratic pedigree that came from his turn as an aide to the late Sen. Daniel Patrick Moynihan of New York.

One of his books, ”Big Russ and Me,” was about his relationship with his father.

On Sunday’s program, Russert was to have interviewed Sens. Lindsey Graham, R-S.C., a national co-chair of the McCain campaign, and Joe Biden, D-Del., an Obama supporter, in a debate format as surrogates for the two presidential candidates. The network said plans for Sunday’s show were now uncertain.

Praise flowed quickly from those who knew Russert across the television interview room.

Senate Majority Leader Harry Reid said Russert was ”the best in the business at keeping his interview subjects honest.”

”There wasn’t a better interviewer in television,” Sen. Barack Obama, the Democratic presidential contender, told reporters in Ohio.

Republican Sen. John McCain of Arizona, Obama’s rival for the White House, hailed Russert as the ”pre-eminent journalist of his generation.”

Rep. John Boehner of Ohio, the House Republican leader, said Russert was ”one of the smartest, toughest television news journalists of all time. … I can say from experience that joining Tim on ‘Meet the Press’ was one of the greatest tests any public official could face.”

Carl P. Leubsdorf, president of the Gridiron Club, an organization of journalists, said in a statement, ”It was a measure of the degree to which Tim Russert was respected in the journalistic world that he was the first broadcaster elected to membership in the Gridiron Club after the rules were changed in 2004 to end our century-old restriction to print journalists.”

”He was an enthusiastic member and a willing participant in our shows. His fellow Gridiron members join with all of those who knew and respected Tim in mourning his untimely death.”

”It is my sad duty to report this afternoon” that Russert collapsed and died while working in the network’s Washington studios, Brokaw said when he came on the air.

”He’ll be missed as he was loved – greatly,” Brokaw said.

The network said on its Web site that Russert had been recording voiceovers for this Sunday’s ”Meet The Press” when he was stricken.

Russert had dozens of honorary college degrees, and numerous professional awards.

He won an Emmy for his role in the coverage of President Ronald Reagan’s funeral in 2004.

He was married to Maureen Orth, a writer for Vanity Fair magazine. The couple had one son, Luke.