BUENOS AIRES -- A federal judge blocked President Cristina Kirchner from using foreign-currency reserves to pay Argentina's national debt and revoked her dismissal of the central-bank chief who opposed that policy.

The twin legal defeats for the government injected further uncertainty in the battle for control of the central-bank reserves. The dispute, which has put Argentina on the verge of a constitutional crisis and placed the president and the opposition-controlled Congress at loggerheads, led to a selloff in the country's...