Anti-war activists consider Watada a hero, but the army accuses him of betraying his fellow soldiers.
Denied a chance to debate the legality of the Iraq war in court, Watada's lawyer on Monday hopes to minimise the amount of time he could serve if convicted.
Watada, the first commissioned officer to refuse specifically to serve in Iraq, has spoken out against US military involvement in Iraq, calling it morally wrong and a breach of American law.
In a video statement in June, Watada said: "As the order to take part in an illegal act is ultimately unlawful as well, I must as an officer of honour and integrity refuse that order."
|"As the order to take part in an illegal act is ultimately unlawful as well, I must as an officer of honour and integrity refuse that order"|
Ehren Watada, US army lieutenant
Despite having already been charged, he spoke out again in August, at a Veterans for Peace rally in Seattle.
Watada said: "Though the American soldier wants to do right, the illegitimacy of the occupation itself, the policies of this administration, and the rules of engagement of desperate field commanders will ultimately force them to be party to war crime."
The lieutenant and his attorney, Eric Seitz, contend his comments are protected speech, but army prosecutors argued his behaviour was dangerous to "the mission" and morale of other soldiers.
Captain Dan Kuecker said at one hearing: "He betrayed his fellow soldiers who are now serving in Iraq."
Colonel Dan Baggio, a US army spokesperson, said: "[It] sets a bad example for the soldiers underneath that person. It sets a bad precedent. At that point in time you've lost good order and discipline. You can't have that in a military organisation."
Seitz unsuccessfully sought an opportunity to argue the legality of the war, saying it violated army regulations that specify wars are to be waged in accordance with the United Nations charter.
His final attempt was quashed last month when the military judge, Lieutenant-Colonel John Head, ruled that Watada cannot base his defence on the war's legality.
Head also rejected claims that Watada's statements were protected by the US constitution's free speech rights.