John McCain will be there, as will Hillary Rodham Clinton, John Edwards and half a dozen other presidential candidates. But when firefighters hold a candidates' forum today in Washington, Rudolph W. Giuliani, the contender most closely identified with their profession, will not attend.

In the past several days, a private tussle over Giuliani's participation — he was out, then in, then out again — has turned into a public spat with the International Association of Fire Fighters. That, in turn, has highlighted an uncomfortable paradox of Giuliani's campaign.

Since the Sept. 11 attacks, when he was mayor of New York City, he has been linked in the public mind to firefighters and police officers, whom he regularly hails as heroes as he campaigns around the country.

Yet the firefighters and police officers who know Giuliani best, those in New York City, have mixed views of him, ranging from admiration to outright hostility.

That has filtered through to leaders of their national associations accusing Giuliani of trying to cut short the effort to find victims' remains in the trade center wreckage.

They also contend that his administration mishandled the development of a radio system that could have saved lives on 9/11, and that he blundered in putting the city's emergency command center in the trade center.

The Giuliani campaign says that the criticism stems from the hostility from union leaders with whom he had tough negotiations, and it promotes the notion that the former mayor has a special bond with emergency workers. He was cheered by firefighters and police officers at recent events in South Carolina and New Hampshire.

"This is a natural constituency for him," said Anthony Carbonetti, a senior Giuliani adviser. The critiques, he said, come from "a select group of union officials, and the union and the firefighters are two different groups of people."

He said rank-and-file workers know, for example, that Giuliani got firefighters heavy-duty suits, known as bunker gear, that has saved lives.

But attacks by emergency workers — quietly encouraged by some rival campaigns — strike at the heart of the candidacy of Giuliani, who presents himself as a leader who tamed crime and led a wounded city through the aftermath of the terror attacks.

The criticism is all the more jarring because most public figures in both parties — whether out of conviction or calculation — have been unwilling to say anything negative about Giuliani's handling of 9/11.

Jim Pasco, executive director of the National Fraternal Order of Police, said: "Everybody likes a Churchillian kind of leader who jumps up when the ashes are still falling and takes over. But two or three good days don't expunge an eight-year record."