Moussaoui is due to go on trial in September
According to government officials and a letter sent to the victim's families, prosecutors will argue that Mr Moussaoui, who is accused of training alongside the 11 September hijackers, should be put to death.
Mr Moussaoui, a French citizen of Moroccan decent, faces six charges including conspiring to commit terrorism, to hijack and destroy planes, and to use weapons of mass destructions.
The government's intention was revealed in a letter from US Attorney Paul McNulty and lead prosecutor David J Novak, which was sent to dozens of victims' families on 7 March.
Victim participation
The letter read: "The Moussaoui case will become a capital prosecution, meaning that the United States will be asking the jury to find that defendant Moussaoui should be executed should he be found guilty."
Prosecutors said they wanted about 30 families to participate in the trial, telling the jury how the attacks had affected them.
According to the letter this testimony would be needed in the punishment phase of the trial if Mr Moussaoui was convicted.
"The individual stories of approximately 30 victims... will serve as a microcosm of all. Obviously, we cannot tell the story of every victim, otherwise the trial would last forever," it said.
Mr Moussaoui's trial is scheduled to begin on 30 September.
Suspect's family quizzed
Stephen Push, whose wife Lisa Raines died in the Pentagon attack, was one of those to receive the letter.
"The prosecutors have been extremely helpful in terms of keeping us informed and I plan to help out in anyway I can," Mr Push said.
On Monday an official from the US prosecutor's office arrived in France to prepare for the trial, officials said.
The official from a federal court in Alexandria, Virginia, travelled to the city of Montpellier in southern France to speak to Mr Moussaoui's family, French judicial officials said.
The US official met with Mr Moussaoui's brother, Abd Samad Moussaoui, who said he would not comply with the US authorities.
The meeting took place at a local police station and afterward Mr Moussaoui's brother said that he had "refused to cooperate" with the official.
"I am viscerally shocked by the fact that I, his brother, and my mother and sister were asked to provide evidence in a proceeding that has for its aim to request the death penalty for my brother," he told France-Info radio.
On Tuesday, the US official was to question the suspect's mother, Aicha, who was to travel to Montpellier from her home in nearby Narbonne.