WASHINGTON, April 12 - Everybody in Washington knows that members of Congress cannot keep secrets. Now two of them are facing questions about whether they inadvertently blew a C.I.A. officer's cover. John R. Bolton, President Bush's nominee to be ambassador to the United Nations, delicately referred to the undercover officer as "Mr. Smith" at his confirmation hearing on Monday. Mr. Bolton, an under secretary of state, was trying to fend off accusations from Democrats that he had tried to get intelligence analysts reassigned because they disagreed with him. One of those about whom that charge was raised now holds an...