A top aide to Attorney General Alberto Gonzales abruptly quit on Friday, almost two weeks after telling Congress she would not testify about her role in the dismissals of federal prosecutors. No immediate reason was given, but Monica M. Goodling's refusal to face Congress had intensified a controversy that threatens Gonzales' job. Asserting her right under the US Constitution not to incriminate herself, Goodling had rejected demands for a private interview with a House committee investigating the firings of eight US attorneys. She was senior counsel to Gonzales and was the department's White House liaison before she took a leave amid the uproar over the ousters. Goodling is at the center of the controversy because, as the bridge between the Justice Department and the White House, she may be best suited to explain how deeply Karl Rove and other members of President George W. Bush's political team might have been involved in the firings.