A Customs and Border Protection program aimed at tightening port security through private self-monitoring is not producing the security it should, a Senate-requested audit shows.

A report released Monday by the Government Accountability Office says the Customs-Trade Partnership Against Terrorism program relies too heavily on self-reported information from those involved. Some 8,000 importers, port authorities, and air, sea and land carriers are getting benefits such as reduced scrutiny of their cargo. In exchange they are required to do inspections of that cargo.

The GAO says that companies can be certified for reduced Customs inspections before they've fully improved their security. The report notes that Customs employees are not required to use third-parties or other security audits.

The report indicates that changes to the C-TPAT program, such as the establishment of minimum security standards and improved methods for validating security practices, have been effective.

Sen. Susan Collins, the ranking Republican on the Senate Homeland Security Committee Ranking Member, requested the report as a means to measure the success of the SAFE Port Act, which she co-authored. She said the report shows that efforts have been achieved at strengthening security of international shipments of cargo to the U.S.

"This report provides a valuable analysis of C-TPAT, which emphasizes private sector efforts and has proven to be a vital component of our nation's overall port security efforts. This program aims to prevent a terrorist from smuggling weapons of mass destruction or other dangerous items into the U.S. in a cargo container, but without disrupting the flow of legitimate trade," she said in a statement.

But Sen. Charles Schumer, D-N.Y., said the Department of Homeland Security has abdicated its responsibilities by permitting private inspections.

"The bottom line is DHS has basically passed the buck on port security by allowing shipping companies to police themselves with almost no oversight," Schumer said. "By not lifting a finger to ensure these companies are doing what they say they are doing, DHS is yet again shirking its primary responsibility. So many years later, it is shocking that DHS still cannot get its act together."

Among the problems:

--A company is generally certified as safe based on its self-reported security information that Customs employees use to determine if minimum government criteria are met. But due partly to limited resources, the agency does not typically test the member company's supply chain security practices and thus is "challenged to know that members' security measures are reliable, accurate and effective."

--Customs employees are not required to utilize third-party or other audits of a company's security measures as an alternative to the agency's direct testing, even if such audits exist.

--Companies can get certified for reduced Customs inspections before they fully implement any additional security improvements requested by the U.S. government. Under the program, Customs also does not require its employees to systematically follow up to make sure the requested improvements were made and that security practices remain consistent with the minimum criteria.

"Until Customs overcomes these collective challenges, Customs will be unable to assure Congress and others that C-TPAT member companies that have been granted reduced scrutiny of their U.S.-bound containerized shipments actually employ adequate security practices," investigators wrote. "It is vital that Customs maintain adequate internal controls to ensure that member companies deserve these benefits."

Customs officials agree they need to do more follow-up on security improvements. In response to the report, CPB issued a statement noting the progress it has made in cargo inspections.

"U.S. Customs and Border Protection has strengthened the security of the global supply chain since the 2005 GAO review and is continuing to make improvements to address potential vulnerabilities. As the GAO recently stated, CBP has made significant improvements to the C-TPAT program’s security criteria, the validation process, staffing and performance measures. As well, CBP has initiated steps to address additional recommendations stemming from the GAO’s more recent review of the program," the statement reads.

The report does make recommendations for additional improvements. For example, GAO recommends that CBP establish a follow-up procedure to ensure that security vulnerabilities identified by CBP officers are addressed on a timely basis by companies in the program.

Click here to read the GAO report. (.pdf)

The Associated Press contributed to this report.