Late Tuesday, Mr. Clapper released a letter of apology to the chairwoman of the Senate Select Committee on Intelligence for what he said were “clearly erroneous” statements during public testimony before the panel in March. At that time Mr. Clapper denied that the N.S.A. collected private data on millions of American citizens, but his statements were proven wrong by the disclosures made by Mr. Snowden.

Mr. Clapper’s apology, made in a June 21 letter to the committee chairwoman, Senator Dianne Feinstein, Democrat of California, came after he admitted, in a television interview earlier in June, that in his testimony he had used the “least untruthful” way to answer a question about domestic surveillance. Mr. Clapper’s statement was made in response to a question from Mr. Wyden, who has made it clear he already knew the answer and was trying to force Mr. Clapper into a public admission on the scope of the domestic collection.

In their letter on Tuesday, Mr. Wyden and Mr. Udall said that before the Internet data collection program was discontinued, American intelligence officials had repeatedly exaggerated its value in classified statements made both to Congress and to a secret court that oversees national security surveillance.

The Internet surveillance program was originally part of a Bush administration program that included the warrantless wiretapping of the phone calls of Americans. But in 2004, the legality of the Internet data collection program so concerned top Justice Department officials that it led to a showdown between the department and White House officials in the hospital room of ailing Attorney General John Ashcroft. After the confrontation the program was briefly stopped, then resumed under a new legal framework. It continued into the Obama administration.

Mr. Wyden and Mr. Udall wrote in their letter that their experience in sparring with intelligence officials over the Internet data program in closed door hearings “has also led us to be skeptical of claims about the value of the bulk phone records collection program in particular.” They said, “It is up to Congress, the courts and the public to ask the tough questions and press even experienced intelligence officials to back their assertions up with actual evidence, rather than simply deferring to these officials’ conclusions without challenging them.”