Assistant U.S. Attorney Michael Ferrara announced the offer in federal court in Manhattan at a pre-trial hearing for Ahmed Abassi.
The plea would be to charges of making false statements and possessing an identification document with intent to defraud the United States. Abassi has pleaded not guilty. The false statements charge carries a maximum of five years in prison while the other charge, a misdemeanor, carries a potential sentence of up to one year in prison.
Ferrara said federal sentencing guidelines would call for a sentence of up to six months in prison if the government declines to ask for a terrorism enhancement at sentencing. If it did, the guidelines would call for six years in prison, he said.
Assistant Federal Defender Sabrina Shroff said her client has not yet decided whether to accept the deal or go to trial. He has been incarcerated without bail since his arrest.
Abassi was arrested at John F. Kennedy International Airport on April 22, 2013, five weeks after he arrived from Canada and began being watched by law enforcement.
Authorities said Abassi met regularly with an undercover FBI agent and with another Tunisian citizen, Chiheb Esseghaier, who later was arrested in Canada in the plot to derail a train that runs between New York City and Montreal.
Prosecutors had claimed Abassi had radicalized Esseghaier, who was charged in Toronto with conspiring with al-Qaida members in Iran in the plot. He is awaiting trial.
Manhattan's top federal prosecutor, Preet Bharara, said a year ago that Abassi wanted to remain in the United States to commit acts of terror and develop a network of terrorists that could use the U.S. as a base to launch international attacks.
Shroff told U.S. District Judge Miriam Goldman Cedarbaum on Tuesday that Abassi was entrapped by the government after an undercover agent provided him with a life of luxury in downtown Manhattan.
She said the government sought to "build up a case that they thought would be the case of the century which never came to bear because Mr. Abassi refused to engage in any concrete plan of terrorism."
Ferrara said the United States does not currently seek to ask for a terrorism enhancement to the sentence if he accepts the deal, but said prosecutors could eventually decide to do so. He also said Abassi would have to agree to be deported if he pleads.
