The suspects had ties with a dangerous Islamic group that once engineered a deadly coup attempt in Trinidad and Tobago, which was approached about underwriting a plot, but in the end, the men decided to stop courting that group and resolved to shop elsewhere overseas for financing.

No one would second-guess the authorities for pursuing and arresting suspected plotters. An enduring lesson that the attacks of Sept. 11, 2001, have taught prosecutors and the Federal Bureau of Investigation is the danger of inaction.

But as with many post-9/11 terror plots, the line between terrible aspiration and reality can get lost in a murky haze.

In case after case, from what authorities said was a dirty bomber to the Lackawanna Six, federal prosecutors hail arrests of terrorists and disruptions of what they describe as sinister plots. But as these legal cases unfold, the true nature of the threats can come into question.

Ms. Mauskopf and Mr. Kelly declined yesterday to discuss their characterizations of the airport case. Mark J. Mershon, assistant director in charge of the F.B.I.’s New York office, also spoke at the news conference, and he said yesterday that his message was very clear:

“I believe I spoke the simple truth at the press conference: the ambitions were horrific, the capacities were very limited, but they kept trying. Their signature was their persistence.”

Neal R. Sonnett, a defense lawyer and former federal prosecutor who was chief of the criminal division in the United States attorney’s office in Miami, congratulated the F.B.I. for fine police work in what was clearly “a prosecutable case.”

But he said: “There unfortunately has been a tendency to shout too loudly about such cases.”

“It has a bit of the gang that couldn’t shoot straight to it,” Mr. Sonnett said. “It would have served the federal government well to say that.”