National Security Agency Director Gen. Keith B. Alexander acknowledged Tuesday that a fact sheet on the agency’s Web site inaccurately described the extent to which the communications of U.S. citizens are protected from the spy agency’s collection of e-mail and other material from technology companies.

The agency removed the four-page document Tuesday after lawmakers raised concerns about its accuracy.

In a letter to Sens. Ron Wyden (D-Ore.) and Mark Udall (D-Colo.), Alexander said he agreed that the fact sheet posted on the NSA Web site last week “could have more precisely described” the requirements governing the collection of e-mail and other Internet content from U.S. companies.

NSA spokeswoman Judith Emmel would not explicitly acknowledge that the fact sheet had been removed from the agency’s Web site. Instead, she referred to the text of a 2008 law that governs NSA surveillance programs.

“Given the intense interest from the media, the public, and Congress, we believe the precision of the source document (the statute) is the best possible representation of applicable authorities,” Emmel said in a prepared statement sent by e-mail to The Washington Post.

The withdrawal of the fact sheet underscores the difficulties the Obama administration has faced in its efforts to reassure the public about surveillance programs that have swept up data on millions of Americans and that operate under legal guidelines that are both classified and complex.

The NSA fact sheet outlined restrictions on a surveillance system known as PRISM, through which the agency has secretly gathered e-mail and other sensitive online material from technology companies including Microsoft, Google, Apple and Facebook.

The program, first described in documents leaked by former NSA contractor Edward Snowden, is supposed to target only “foreign persons” located outside the United States. But Wyden and Udall sent a letter last week to Alexander questioning some of the agency’s claims.

The fact sheet “portrays protections for Americans’ privacy as being significantly stronger than they are,” the letter said. It also said that the document’s description of “minimization” procedures designed to protect Americans against privacy intrusions were “somewhat misleading.”

The senators did not elaborate on their objections or specify which statements they believed overstated privacy protections.

The fact sheet asserted broadly that the program “allows only the targeting . . . of communications of foreign persons who are located abroad.” In his reply letter, Alexander acknowledged that the law allows for “the targeting of persons reasonably believed to be located outside the United States.” That language leaves a fair amount of discretion to analysts to determine whether a person is overseas.

The exchange over the document is the latest instance in which senior lawmakers have challenged U.S. intelligence officials over their characterizations of the NSA programs. This month, Director of National Intelligence James R. Clapper Jr. acknowledged that he had given what he called the “least most untruthful” response when he testified in March that the NSA does not collect data on millions of Americans.