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, that intelligence veterans and civil libertarians fear could be counterproductive and may raise constitutional issues.

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.

Meanwhile, Mitt Romney, the presumed presidential nominee, and other Republicans have added an election-year spin to old Washington tussles over government secrecy, accusing the White House of leaking secrets to enhance President Obama’s image. Mr. Romney has sought to taint the centerpiece of Mr. Obama’s security record, the killing of Osama bin Laden, calling White House disclosures about the raid in Pakistan “contemptible.”

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. But on the Senate floor on Wednesday, Senator John McCain, Republican of Arizona, suggested that the F.B.I. was foot-dragging and should zero in on high-level Obama administration officials.

READ MORE: NY TIMES