The SEC, which is responsible for policing Wall Street, destroyed internal documents that should have been preserved as official federal records, the agency’s inspector general has found.

The SEC also withheld important information about the practice from the National Archives, according to the inspector general. The Archives oversees the preservation of federal records and last year asked the Securities and Exchange Commission to address an allegation that the SEC had destroyed documents without authorization.

An Archives official concluded that the SEC’s August 2010 explanation appeared to be “inaccurate or misleading,” the inspector general’s report said.

From about 1981 to mid-2010, it was SEC policy to dispose of all documents related to inquiries into potential wrongdoing that did not lead to full-fledged SEC investigations, the inspector general’s office said in the report released Tuesday. Since 1992 alone, more than 10,000 inquiries fit that description.

One of the files involved an anonymous tip about Lehman Brothers Holdings written on the letterhead of Lehman’s auditor, Ernst and Young, the report said.

Lehman’s collapse in 2008 brought the international financial system to the brink of collapse. Since then, New York’s attorney general has filed a lawsuit against Ernst and Young, alleging that the accounting firm helped Lehman hide billions of dollars of liabilities.

Ernest and Young has defended its work for Lehman, saying the firm believes it “met all applicable professional standards.”

The SEC opened its file on the anonymous tip about Lehman in March 1992 and closed it four months later. Although some SEC records related to the file survived on an agency computer drive despite the document destruction policy, others — including the original tip — can no longer be located, the inspector general reported.

Other files apparently destroyed related to Bernard Madoff, who is serving a 150-year prison sentence for running a massive Ponzi scheme.

Since the allegations of improper document destruction came to light, the SEC has said that an electronic database still contains information about purged files. However, the inspector general’s office found only sketchy or unclear information about certain files in which Madoff was listed as a “Related Name,” the report said.

For example, the electronic entry for an inquiry closed in 1994 says “Inappropriate for Enforcement Action.”

The purged documents could have helped outsiders hold the SEC accountable for decisions not to pursue particular cases, and they could have helped agency investigators connect the dots if later suspicions arose involving the same parties, said Gary Aguirre, an attorney for the SEC employee who blew the whistle on the document destruction.

The report, signed by SEC Inspector General H. David Kotz, said the inspector general’s office was not aware of any investigation that was hampered by the destruction of records, but he noted that he had not conducted an exhaustive review of the impact.

It is unclear why the SEC adopted the document destruction policy, Kotz said.

In a statement, SEC spokesman John Nester said that the agency was pleased that the inspector general found “no evidence of any improper motive on the part of current or former SEC staff.”

“As the report notes,” Nester said, “the old policy was discontinued when the National Archives and Records Administration voiced concerns.”

The inspector general’s probe was triggered by Darcy Flynn, a lawyer in the SEC’s enforcement division, who alerted the Archives last year to document destruction.

The Archives then sought an explanation. After a drafting effort that involved several SEC officials, the SEC responded that the agency was “not aware of any specific instances of the destruction of records” from the initial inquiries.

That response neglected to mention that it was SEC policy to “to destroy all such documents” when the files were closed, Kotz wrote. At the time the SEC sent that response, enforcement officials knew of at least one specific instance of destroying records because an enforcement official had alerted the staff that she had recently shredded documents and deleted e-mails at the agency.

The SEC’s August 2010 response to the Archives “did not comply with federal regulations,” the inspector general found. In drafting the letter, the SEC might have been motivated by “fear of criminal exposure for the SEC,” the report said.

While it was drafting the response, the SEC made no effort to get to the bottom of what happened, the report said.

The SEC “seemed to spend more time covering tracks and drafting a lawyered-up response than just following the law and otherwise using common sense,” Sen. Charles E. Grassley (R-Iowa), who has sought answers from the SEC about the document destruction, said in a statement Tuesday.

When officials at the SEC learned what Flynn had told the Archives, they told Flynn that he should no longer speak directly to the Archives, the report said.

In September, Flynn and his attorney alleged that the improper document destruction was ongoing a year after he first raised the issue and that it involved a wider variety of investigative records than he originally alleged.

The inspector general’s office said it may investigate those allegations further, and it recommended that the SEC seek guidance from the National Arches on which documents must be preserved.