WASHINGTON — The National Security Agency has told Congress that it has forced out a civilian employee after a lengthy investigation to “assign accountability” for the disclosure of intelligence secrets by Edward J. Snowden, one of its former contractors.

Two others — identified only as an active-duty military member and another contractor — were “removed from access to N.S.A. information” and facilities last August. But because neither worked directly for the N.S.A., the agency told the House Judiciary Committee in a letter, any further action would have to be determined by their employers.

The letter, first reported by NBC News, was intended to answer congressional queries about who, beyond Mr. Snowden himself, would be held accountable for the security lapses that led to his disclosures. The answer appeared to suggest that no senior officials of the N.S.A. or its oversight organization, the office of the director of national intelligence, will be disciplined or fired for what officials have called the largest and most damaging disclosure of classified material in American history.

The director of the N.S.A., Gen. Keith B. Alexander, is retiring next month after serving far longer than his predecessors. The director of national intelligence, James R. Clapper Jr., who has also been a focus of criticism for failing to police the speed at which security upgrades have been conducted throughout the intelligence community, remains in office.