Judge Barbara Caulfield criticised British security forces in Northern Ireland, which she said systematically harmed and imprisoned Irish nationalists accused of offences against them. At a hearing in San Francisco, she shifted the burden of proof away from Mr Smyth, a 39-year-old Belfast man, who fled to the US after a republican mass break-out from the Maze prison in Northern Ireland 10 years ago.
In pre-trial extradition proceedings, his lawyer argued that he should not be returned because he faces the risk of political persecution. The judge decided it will now be up to the British authorities to prove that this is not the case.
Her order came after Sir Patrick Mayhew, Secretary of State for Northern Ireland, refused to supply the court with government documents about the security forces in Northern Ireland.
The case is being seen as a test of the revised extradition treaty between Britain and the US. The treaty was amended in 1986 to include a clause that allows US courts to refuse to extradite anyone who may be at risk of political or religious persecution.