Rep. Darrell E. Issa, California Republican and chairman of the Oversight and Government Reform Committee, said his staffers have come across verbal and written policies from the Office of Personnel Management that indicate the security clearance process was short-circuited in the case of Aaron Alexis, the Navy Yard shooter.

But Mr. Issa says OPM is refusing to turn over those documents and allowing them to be viewed only behind closed doors. If he doesn’t have the documents by noon Thursday, he said, he will issue a subpoena.

Mr. Issa said he thinks the agency is trying to protect itself from embarrassment from questions about the clearance process for Alexis and for Edward Snowden, the former contractor whose leaks have exposed some of the government’s most secret spy programs.

“These policies include the failure to secure arrest records that would have alerted federal officials to his violent past,” Mr. Issa wrote in a letter, obtained by The Washington Times, which was sent Wednesday to OPM Director Katherine Archuleta. “Perhaps most disconcerting, though, is OPM’s indifference to obtaining all the relevant information about individuals under review for a security clearance.”

Mr. Issa said his investigators also have seen an OPM training presentation that offered tips on “how to complete a thirty day caseload in less than thirty days.”

That same document also told those conducting the security review that when looking for criminal records, local law enforcement officers “either got ‘em, or they don’t.” Mr. Issa said that “cavalier” guidance made it seem like it was acceptable not to fully pursue those records.

That matters because, in the case of Alexis, security clearance investigators failed to turn up information about an arrest and failed to uncover accusations that he used a gun to shoot at a vehicle’s tires.

Mr. Issa is seeking all training materials, the contracts with third-party companies that help with the screenings, and information on how the screeners’ job performances are assessed.

In an earlier letter to Mr. Issa, OPM’s chief attorney said the agency was withholding documents because some of them contain sensitive business information and others, if made public, would lay out clear ways to defeat the clearance system.

OPM also hinted that it could claim to protect the documents by executive privilege because they implicate the White House budget office’s interests.

Spokeswoman Lindsey O’Keefe said Wednesday that the agency believes it has given access to Mr. Issa’s investigators.

“We have already made these documents available to the committee for review. We have received Chairman Issa’s most recent letter dated November 20, 2013, and plan to respond to him as appropriate,” Ms. O’Keefe said in an email.

The method of granting security clearances has become a heated topic this year, with several congressional committees vowing to review the procedures in the wake of the Navy Yard shooting and the Snowden leaks.

Mr. Issa said the fact that the government and its contractors cleared Alexis and Mr. Snowden “enabled them to carry out their heinous acts.”