WASHINGTON — The chairwoman of the Senate Intelligence Committee emerged from a classified briefing on Thursday about the leak of top secret surveillance programs and declared that Congress would soon consider legislation to sharply limit the access that private contractors — who operate much of the national security infrastructure — have to the nation’s most sensitive intelligence programs.

“We will certainly have legislation which will limit or prevent contractors from handling highly classified and technical data, and we will do some other things,” the chairwoman, Senator Dianne Feinstein, said after a review of the episodes attended by almost half of the members of the Senate.

Ms. Feinstein, a California Democrat, said that on Monday the National Security Agency would release more information about the potential terrorist attacks that had been thwarted by its surveillance programs. “There are more than you think,” she said a bit cryptically. The senator has been among the most vocal defenders of the program.

Earlier in the day, the security agency director, Gen. Keith B. Alexander, vowed to clear up what he said were inaccuracies and misperceptions about what kind of data the agency collects, and how it uses it. But the disclosure of any further detail, he said, would have to navigate a delicate line between the public’s right to know and divulging material that could tip off enemies.