The demonstrators are to include Daniel Ellsberg, the former Defense Department analyst who leaked the Vietnam War records known as the Pentagon Papers; gay veteran Lt. Dan Choi, a national leader in the campaign to end Don't Ask, Don't Tell; and busloads from the Occupy Wall Street and Washington encampments.
Espionage Act. If convicted, he could be sentenced to life in prison.
Manning is suspected of leaking field reports from Afghanistan and Iraq, diplomatic cables that included analyses and observations of foreign leaders and governments, and video footage of a 2007 helicopter attack that killed 12 in Baghdad.
The Article 32 hearing is to be Manning's first appearance since his May 2010 arrest in Iraq. It will also mark his return to Maryland; he lived in Potomac and studied at Montgomery College before he enlisted in the Army in 2007.
An independent officer will hear testimony and arguments before making a recommendation on whether to send the case to court-martial. The hearing is expected to take five days.
The release of the Apache helicopter video, in which Americans can be heard laughing and referring to Iraqis as "dead bastards," has made whoever leaked it a hero to antiwar activists.
They say that video and the other materials were incorrectly and illegally classified, and that whoever disclosed it should be protected as a whistle-blower.
"It was very important that that information be out," Jean Athey, an activist from Montgomery County, said Thursday. "Making information public is essential to a free country."
Organizers with the Bradley Manning Support Network say hundreds will participate in a vigil on Friday and a march and rally on Saturday. They say more than 50 demonstrations will take place around the world on Saturday, Manning's 24th birthday.
"We would like to see Bradley Manning freed," Baltimore peace activist Max Obuszewski said. "He's in jail because he exposed some what I would consider illegal and definitely unwarranted activities by my government.
"Regardless of what happens at this hearing or at the eventual court-martial, we'll still be acting to get him out of there."
Manning's detention at the Marine Corps base in Quantico, Va. — where he was held from July 2010 until April of this year in a maximum-security, single-occupancy cell, placed on a prevention-of-injury order and allowed to wear only a suicide-proof smock at night — drew concern from Amnesty International and a request to visit from a United Nations torture investigator.
Manning was moved in April to Fort Leavenworth in Kansas.
Athey and Obuszewski were two of 33 demonstrators who were arrested outside the Quantico base in March. Athey called the treatment of Manning "astonishingly horrific."
"It's important for people to go [to Fort Meade] and show support for him and show that we're watching and we're aware of what the government is doing and it's not what our country is about," she said.
President Barack Obama and Pentagon officials have defended the conditions of his detention.
Fort Meade is one of three bases within the Military District of Washington that have a courtroom that can accommodate the proceeding, according to a spokeswoman.