Defreitas was arrested a short time later, as was Trinidadian Kareem Ibrahim.
The suspect at large is Abdel Nur of Guyana.
The United States is seeking the extradition of Kadir and Ibrahim. All four men could face life in prison if convicted.
The aim of the plot, officials said, was to cripple the United States economically and psychologically by blowing up pieces of Kennedy's elaborate jet fuel storage and pipeline system, which stretches across several of the city's boroughs through New Jersey to a supply point in Allentown, Pa.
JFK is among the world's busiest airports, with about 1,000 flights a day. It is expected to handle 45 million passengers and 1.5 million tons of cargo this year.
Much of the federal case cites information obtained with the help of an FBI informant, who is not named in the complaint but is described as having been convicted of drug trafficking and criminal conspiracy. The informant's sentence for his latest conviction "is pending as part of his cooperation agreement with the government," according to the 33-page complaint filed Friday and unsealed Saturday.
The complaint says Defreitas had greeted the informant and a companion at a mall, saying he recognized them from a Brooklyn mosque. Defreitas and the informant met on occasions after that, and eventually Defreitas invited him into the plot, the complaint says.
The two are described as making four visits to JFK together in January to conduct surveillance and make videotapes of potential targets. The two also traveled to Guyana together, the complaint says.
The complaint alleges efforts to tap Muslim extremists from the United States, Guyana and Trinidad, including the Jamaat al Muslimeen, a group that staged a coup attempt in Trinidad and Tobago in 1990. It says the men tried to solicit money, expertise and technical help from overseas contacts.
The FBI informant recorded conversations with Defreitas, the complaint says. In one section, Defreitas is quoted as describing his desire to launch a strike that would surpass the impact of the Sept. 11 attacks, and explains that his former job gave him "unique knowledge of the airport." In other conversations, the complaint alleges, Defreitas described being angered while working at JFK to see military parts being shipped to Israel "that he felt would be used to kill Muslims."
Defreitas also spoke of the psychological effect on Americans of striking at JFK, the complaint says, quoting him as saying: "Anytime you hit Kennedy, it is the most hurtful thing to the United States. To hit John F. Kennedy, wow.... They love John F. Kennedy like he's the man.... If you hit that, this whole country will be in mourning. It's like you can kill the man twice."
The complaint alleges that Defreitas and others gathered information on the airport by such methods as making videotapes of areas where planes were parked, and downloading satellite images from Google Earth to map the airport's layout.
According to the complaint, Defreitas also made repeated trips to Guyana in recent months to try to enlist help from Kadir and others to carry out the attack, which the complaint said Kadir code-named "the chicken hatchery" or "chicken farm."
Defreitas "had some ideas" about what he wanted to do, said the U.S. law enforcement official who spoke on condition of anonymity. "But he was a long way off from being operational or even coming close to getting explosives or posing a direct threat to JFK." The official characterized the seriousness of the plot as "a notch below Ft. Dix" -- the recent case in which six Muslim men in New Jersey were charged with planning an attack on the Army base.
In the complaint, at least a dozen other people are mentioned but not named who are believed to have been connected to the plot or in contact overseas with Defreitas. They are being sought for questioning, officials said.
"We had hopes to get a lot more people, but they are still at large," the U.S. law enforcement official said. "They're not charged, but they are still involved."