WASHINGTON - They've been an unlikely pair since the day they met - the nerdish bookworm and the cocky backslapper - but Karl Rove and George W. Bush have been partners and political allies for more than 30 years. Now their friendship is being tested by Rove's involvement in the unauthorized outing of an undercover CIA officer. Depending on the outcome of a grand jury investigation, the president soon could face a painful choice between protecting his trusted aide or forcing his resignation to limit political damage. ''It's going to be an interesting test of his loyalty if this goes...