Director of National Intelligence James Clapper (J. Scott Applewhite/AP)This may be as close as a sitting U.S. senator comes to publicly calling the director of national intelligence a liar.

Sen. Ron Wyden, D-Ore., a Senate Intelligence Committee member and sharp critic of government domestic surveillance programs, warned DNI James Clapper on Tuesday that he must give "straight answers” to lawmakers about the extent of spying on Americans. Wyden also made it plain that he doesn’t think Clapper offered up the whole truth in a March hearing of the committee.

The back-and-forth began in March when Wyden asked Clapper: "Does the NSA collect any type of data at all on millions or hundreds of millions of Americans?" Clapper replied: "No, sir." Wyden followed up: "It does not." Clapper went on: "Not wittingly. There are cases where they could inadvertently perhaps collect, but not wittingly."

In the aftermath of the revelation that the NSA vacuums up the telephone records of millions of Americans with near-routine frequency and has programs for the surveillance of Internet activity, Clapper has tried to banish the impression that he misled Congress. The spy chief's main defense appears to be rooted in the intelligence community's technical definition of "collect," which basically requires that an analyst process the information scooped up by other means. (This document, obtained by the Federation of American Scientists, puts it slightly differently: "Data acquired by electronic means is 'collected' only when it has been processed into intelligible form.")

Wyden isn't buying it. And the senator noted in his statement that he had sent the question to Clapper a day in advance.

"One of the most important responsibilities a senator has is oversight of the intelligence community. This job cannot be done responsibly if senators aren’t getting straight answers to direct questions," Wyden said.

"So that he would be prepared to answer, I sent the question to Director Clapper’s office a day in advance. After the hearing was over, my staff and I gave his office a chance to amend his answer," the lawmaker said. "Now public hearings are needed to address the recent disclosures, and the American people have the right to expect straight answers from the intelligence leadership to the questions asked by their representatives.”