Nutter said later in the day that he would have continued his delivery, inaudible in chambers, had Clarke not called a recess. But the mayor refused to second-guess that decision.
"I'm a guest. . . . It's their house," he said. "It's not for me to decide or opine on what should have been done. I just came to give a speech."
The mayor said he was never concerned for his safety. He was mostly "dismayed" at the affront to Council and its chambers - "its grandeur and its history just deserves a certain amount of respect."
The administration and Council had been discussing for days the potential for municipal workers to disrupt the speech. Last year they catcalled and heckled Nutter throughout.
The mood among the unions has only soured since, as Nutter challenged a second arbitration award for firefighters and sought to impose a contract on blue-collar workers.
"This morning was fully anticipated," Clarke said. "I think the unions came here today with the intent of not letting the mayor have his budget message."
But Clarke said there was no plan to recess the meeting in that event. Nutter seemed taken aback when Council members began straggling out of the chamber while he was speaking.
"It got to the point today that was extremely nonproductive," Clarke said. "At some point, you have to take an action to bring that to some conclusion."
Clarke said he never considered trying to clear the chamber so Nutter could continue because some union members had expressed a willingness to be arrested.
"I think the worst thing that could happen is to have the police come in force and arrest a group of municipal workers who are simply trying to get a contract," he said.
Clarke brushed off concern that the unions were disrespectful to Council, but said that because the contract fight had spilled into chambers "in a very aggressive way," he was going to "get engaged" in the negotiations.
Clarke would not say how or why he thought he could mediate - an "unprecedented endeavor," he said - except to describe the dispute as a "very, very resolvable situation."
"From what I understand of the issues, they're relatively close," he said.
Nutter said he had not discussed Clarke's intention to insert himself into the talks and was not sure what he would bring to the table.
"If he has some additional ability to cause them to have a full conversation about pensions and health care and work rules and overtime calculation and furloughs, that would be great," Nutter said. "But at the end, the only person who can sign a contract is me."
Of Philadelphia's four municipal unions, only the Fraternal Order of Police has a current contract, awarded in arbitration.
The firefighters got a three-year contract, also through arbitration, but the Nutter administration has appealed it twice in the courts, arguing the city cannot afford its terms.
Nonuniformed workers, represented by AFSCME District Councils 33 and 47, have been without a contract since 2009. Nutter wants a pact that would send new employees into a less-expensive pension plan, allow workers to be furloughed, and change work rules to reduce overtime.
In January, the administration said talks with D.C. 33 had reached an impasse and asked the state Supreme Court for permission to impose its last offer.
The Supreme Court has not yet agreed to consider the case, but public employee unions throughout the state have filed briefs attacking the city's action.
City Budget Director Rebecca Rhynhart said the new budget proposal includes $26 million for unresolved contracts with D.C. 33, D.C. 47, and the firefighters - enough to fund the city offers to each union, including raises of at least 2.5 percent.
Riled union members began arriving at City Hall three hours before the Thursday morning address, many carrying placards depicting Nutter as Bozo the Clown, while the ubiquitous union inflatable rat circled the building on the back of a truck.
Nutter entered the chamber to a deafening response of whistles and chants that showed no sign of abating. The mayor nonetheless placidly began reciting his speech into the microphone.
Clarke pounded his gavel and huddled briefly with Nutter, who returned to the microphone. The mayor only left the room after it was clear Council had gone into recess.
The scene was reminiscent of 2004, when hundreds of employees staged a sit-in that halted a Council meeting for five hours.
The unions had been without a contract for four months at that point, and also were protesting business tax cuts seen as draining money that could cover their raises. Nutter, then a councilman, was a major proponent of the cuts.
The demonstration ended after then-Mayor Street promised to work around the clock to resolve the contracts. Some Council members accused Street of orchestrating the entire show.
Street, Clarke's former boss and longtime mentor, attended Thursday's budget address - as he does every year - with students from his government class at Temple University.
After Nutter and Council vacated the chamber, Street stood fielding questions. He said he was not surprised by Nutter's reception.
"The labor situation that we have today is untenable," said Street. "The mayor's in the Supreme Court saying, 'I don't have to negotiate with you.' . . . That's more troubling to them than just the fact that they don't have a contract."
Bill Green, who was one of the few members who remained in the chamber, said the meeting should not have been recessed. Green also was the only member who went downstairs to hear Nutter's uninterrupted speech.
"This is outrageous," said Green, to date Nutter's chief critic in Council. "Michael Nutter is the mayor of the city of Philadelphia. I don't care what you think of him, you have to give the office respect."
To see a video of Thursday's raucous Council meeting, go to www.philly.com/downshout
Contact Troy Graham at 215-854-2730 or firstname.lastname@example.org. Follow on Twitter @troyjgraham.