An American-born Taleban fighter imprisoned in Indiana will try to convince a federal judge that his religious freedom trumps security concerns in a closely watched trial that will examine how far prisons can go to ensure security in the age of terrorism.

John Walker Lindh was expected to testify today in Indianapolis during the first day of the trial over prayer policies in a tightly restricted prison unit where he and other high-risk inmates have severely limited contact with the outside world.

Lindh, 31, a Muslim convert who was charged with supporting terrorists after he was captured by US troops in Afghanistan and later pleaded guilty to lesser charges, claims his religious rights are being violated because the federal prison in Terre Haute, Indiana, deprives him of daily group prayer.

Muslims are required to pray five times a day, and the Hanbali school to which Lindh belongs requires group prayer if it is possible. But inmates in the Communications Management Unit are allowed to pray together only once a week except during Ramadan. At other times, they must pray in their individual cells. Lindh says that doesn't meet the Koran's requirements and is inappropriate because he is forced to kneel in close proximity to his toilet.

The American Civil Liberties Union of Indiana, which is representing Lindh, contends the policy violates a federal law barring the government from restricting religious activities without showing a compelling need.

"This is an open unit where prisoners are basically out all day," said ACLU legal director Ken Falk, noting that inmates are allowed to play basketball and board games, watch television and converse as long as they speak English so the guards can understand.

"They can do basically any peaceful activity except praying," he said. "It makes no sense to say this is one activity we're going to prohibit in the name of security."

Joe Hogsett, the US attorney for the Southern District of Indiana, said he believes decisions about prison regulations are best made by prison officials, "not by convicted terrorists and other dangerous criminals who reside there".

"Mr Lindh is allowed to pray in his cell; he's allowed to pray wherever he happens to be as many times every day as his religion suggests to him that he should," Hogsett said. "Where the rules must draw the line is how often must prison officials allow prisoners to congregate together?"

Attorneys representing the government maintain that Lindh's own behaviour since he was placed in the unit in 2007 proves the risks of allowing group prayer.

The government says in court documents that Lindh delivered a "radical, all-Arabic sermon" to other Muslim prisoners in February that was in keeping with techniques in a manual seized from al Qaeda members that details how terrorists should conduct themselves when they are imprisoned.

Lindh's sermon proved "that religious activities led by Muslim inmates are being used as a vehicle for radicalisation and violence in the CMU", the government claimed.

Falk said Lindh's speech wasn't radical and was given during the weekly prayer that inmates are permitted. He said Lindh was not disciplined for the speech.

The self-contained unit in which Lindh resides has 43 inmates, 24 of whom are Muslim. Inmates are under open and covert audio and video surveillance, and except for talks with their attorney, all of their phone calls are monitored. Prisoners are not allowed to touch their family members when they come for their tightly limited visits. They must speak English at all times except when reciting ritual prayers in Arabic.

Without such tight security, the government claims, the prisoners would be able to conspire with outsiders to commit terrorist or criminal acts.

According to court documents, daily prayers were allowed from the time the unit opened in 2006 until May 2007, when Muslim inmates refused to stop in the middle of a prayer to return to their cells during a fire emergency.

The lawsuit was originally filed in 2009 by two Muslim inmates in the unit. Lindh joined the lawsuit in 2010, and the case has drawn far more attention since then. The other plaintiffs have dropped out as they were released from prison or transferred to other units.

Thomas Farr, a former diplomat who now teaches at Georgetown University and studies religion and terrorism, said common sense suggests that the prison's need for security would outweigh Lindh's religious rights.

Stanford University terrorism expert Martha Crenshaw said prison officials have legitimate security concerns but questioned how dangerous Lindh really was, noting that he was not a leader or an influential cleric. Even the government says Lindh is currently characterised as a minimum-security prisoner.

He had been charged with conspiring to kill Americans and support terrorists, but those charges were dropped in a plea agreement. He is serving a 20-year sentence for supplying services to the now-defunct Taleban government of Afghanistan and carrying explosives for them and is eligible for release in 2019.

"The fact that the charge of conspiring to kill Americans was dropped could be considered evidence that he was not a personally violent jihadist," Crenshaw said in an email.

"Certainly after 9/11 the pendulum has swung toward preventing terrorism at almost any cost," Crenshaw said. "I would like to think that it could be swinging back, but it swings slowly. Once established, routines are hard to change."

- AP