A Department of Homeland Security plan to require port workers to carry tamperproof photo ID cards has numerous security problems that threaten to delay it, investigators said Thursday.

In an audit, Homeland Security Inspector General Richard Skinner said his review of prototype systems at participating U.S. ports identified vulnerabilities in the Transportation Worker Identification Credential program, known as TWIC.

The weaknesses, some of which were deemed high risk, included instances of false positives in detecting which workers might pose a security risk as well as cases in which the system inadvertently disclosed sensitive personal information inappropriately.

Portions of the report were redacted to prevent public disclosure of specific weaknesses.

"TWIC prototype systems are vulnerable to various internal and external security threats," Skinner wrote. "Until remedied, the significant security weaknesses jeopardize the certification and accreditation of the systems prior to full implementation of the TWIC program."

In written responses, the Transportation Security Administration, which runs TWIC, said that it had expected to encounter some problems with its test program, appreciated the input and was now working to fully address concerns.

"It was acknowledged in discussions with (Skinner) that a prototype system will always need further enhancements and additional work to ready it for production," wrote TSA deputy assistant secretary Robert Jamison.

Congress ordered the administration to develop the card as part of port security legislation passed in late 2002. Under the plan, the TSA would collect biographical information including fingerprints, name, birthdate, address and phone number, alien registration number if applicable, photo, employer and job title.

Before issuing a card, the government would conduct a background check on the worker, including a review of criminal history records, terrorist watch lists, legal immigration status and warrants. In May, Homeland Security said it would soon ask outside contractors to bid on handling the project.

In his audit, Skinner recommended that TSA create a formal office to oversee TWIC security to ensure weaknesses are fixed.

The program at first is expected to cover 750,000 workers who have unescorted access to secure port areas, including longshoremen, port employees, truck drivers and rail workers.