WASHINGTON -- A federal judge shut down the first American military commission since World War II yesterday, ruling that the Bush administration violated the Geneva Conventions in its handling of prisoners at the Guantanamo Bay prison.

The ruling, the first test of a US Supreme Court decision in June granting legal recourse in civilian court to the 550 or so ''enemy combatants" being held at Guantanamo, delivered a new legal blow to President Bush's unorthodox war on terrorism policies.