Federal agencies should take better care of Social Security numbers in order to protect people's privacy, congressional investigators said Monday.

Researchers said the unique identification numbers — which are key to protecting against identity theft — can be found on public documents at all levels of government.

Investigators said the numbers are even more common on public records in state and local governments, such as professional licenses and property titles.

"Officials who maintain these records told us their primary responsibility is to preserve the integrity of the record rather than protect the privacy of the individual SSN holder," said researchers at the General Accounting Office, the investigative arm of Congress.

Social Security numbers, designed only to help the government keep track of earnings and benefit information, are now used for almost every government transaction and on many private documents.

Because of their ubiquity, the numbers are often used in identity theft, in which a perpetrator opens fraudulent credit card, bank loan and other accounts in a victim's name. With a Social Security number, a person can apply for additional false documents, like a driver's license.

The Social Security Administration said Social Security number misuse increased from about 11,000 during the 1998 fiscal year, which ended Oct. 31, to 65,200 incidents in 2001.

Officials blame the Internet and electronic record-keeping for the explosion in crimes.

"Although few entities report making SSNs available on the Internet, several officials told us they are considering expanding the volume and type of public records available on their Web site," the report said.

The report notes the ways governments are trying to protect privacy, such as editing the number out on public copies of documents, but protection is haphazard. Government agencies are not always telling the public how their Social Security numbers may be used.

That warning, mandated by law, "is the first line of defense against improper disclosure because it allows SSN holders to make informed decisions," the report said.

Congressional investigators said the White House's Office of Management and Budget, which advises government agencies on how to handle privacy issues, should tell the agencies to review how they deal with Social Security numbers and clarify that federal privacy law applies to local governments as well.

According to the report, White House officials said they "are unsure of the need for additional OMB guidance in this area."

The GAO said Congress should create a commission to develop a unified approach to safeguarding Social Security numbers.

A bill introduced by Sen. Dianne Feinstein, D-Calif., would require Social Security numbers to be removed from government checks and driver's licenses and ban release of certain public documents without Social Security numbers removed, including death and birth certificates and tax liens.