The Justice Department issued a broad defense Tuesday of an investigative tool used by the FBI to compel businesses to turn over customer information without a court order or grand jury subpoena.

Questions about the use of National Security Letters have become caught up in the debate over renewal of the anti-terror Patriot Act, which has been delayed by ideologically diverse lawmakers who want to ensure there are checks on investigative powers. More than a dozen provisions of the law, which was passed in the wake of the Sept. 11 attacks, expire at the end of the year.

NSLs, which can be used in terrorism and espionage investigations, require telephone companies, Internet service providers, banks, credit bureaus and other businesses to produce highly personal records about their customers or subscribers.

While most information about the letters is classified, including the number of times they have been used, Assistant Attorney General William E. Moschella sent the chairmen of the House and Senate Judiciary Committees a 10-page letter rebutting criticisms aired in an article three weeks ago in The Washington Post.

The article, citing sources, said the FBI issues more than 30,000 NSLs a year, up from a few hundred prior to the Sept. 11, 2001, attacks. Moschella said the number was among several "erroneous claims" in the article, but he offered no alternative.

Justice Department officials previously gave lawmakers closed-door briefings on the security letters, where they shared the number.

Also false, according to Moschella, is the claim that the FBI uses NSLs to spy on law-abiding Americans.

But he acknowledged that some people whose records are produced "may not be terrorists or spies or associated with terrorists or spies."

Lisa Graves, a lawyer for the American Civil Liberties Union, said that despite Moschella's admission, the government is allowed to retain that information. "I think the American people would prefer that there be some sort of connection and if not, then the records ought to be destroyed," Graves said.

A tentative agreement between House and Senate negotiators to renew the Patriot Act contains several provisions involving NSLs, including requirements that the Justice Department report publicly on the number of NSLs and that recipients be allowed to consult a lawyer.

The Bush administration contends that such consultation already is allowed, citing at least two court challenges to NSLs. However, in a letter obtained by the ACLU under the Freedom of Information Act and posted on its Web site, the FBI prohibits the recipient "from disclosing to any person that the FBI has sought or obtained access to information or records under these provisions."