Mr. Cuomo, in his public remarks, went a bit further.

“We would be in a state of denial if we did not say, with what’s going on internationally, that the risk of a threat to us has increased,” said Mr. Cuomo, a Democrat seeking a second term in November.

“But we’re not in a state of denial,” he added, taking a reassuring tone. “We’re in the state of New York.”

Although the mood was mostly stoic, the politicians did find some mutual laughs at the expense of their shared agitator: the news media. When a reporter from NY1 asked Mr. Christie about Mitt Romney and foreign affairs, the Republican governor — who is pondering a presidential bid of his own — let loose with a trademark riposte.

“You will not be the least bit surprised that there is no chance, zero chance, that I will answer an off-topic question,” Mr. Christie said with a smile, prompting Mr. Cuomo, a skilled, if slightly subtler deflector himself, to laugh aloud and clap his hands.

Mr. de Blasio, a Democrat who as a first-term mayor is new to these sorts of security briefings, easily adapted, if with a touch of characteristically cosmic rhetoric.

“We understand the moment in global history,” he said. “We understand the need for vigilance. How we address that is with extraordinary collaboration and teamwork and with the kind of support from the federal government that is exemplary for the times we are living in.”

The mayor is still in the process of being approved for federal security clearance, The New York Post reported last week. That process can often take months, and the mayor’s police commissioner, William J. Bratton, who also attended the session, does have clearance. Last week, the mayor said, “The practical reality is that in the event of an emergency, the appropriate information will be shared with decision makers.”