F.B.I. agents on a hunt for leakers have interviewed current and former high-level government officials from multiple agencies in recent weeks, casting a distinct chill over press coverage of national security issues as agencies decline routine interview requests and refuse to provide background briefings. The criminal investigation, which has reached into the White House, the Pentagon, the National Security Agency and the C.I.A., appears to be the most sweeping inquiry into intelligence disclosures in years. It coincides with Senate consideration of new legislation designed to curb intelligence officials' exchanges with reporters. The legislation approved last week by the Senate Intelligence Committee would reduce to a handful the number of people at each agency permitted to speak to reporters on background," or condition of anonymity; require notice to the Senate and House intelligence committees of authorized disclosures of intelligence information; and permit the government to strip the pension of an intelligence officer who illegally discloses classified information. The Obama administration has set a record for prosecuting leaks of classified information to the news media, with six cases to date, more than under all previous presidents combined. The F.B.I. appears to be focused on recent media disclosures on American cyberattacks on Iran, a terrorist plot in Yemen that was foiled by a double agent and the so-called "kill list" of terrorist suspects approved for drone strikes.