The government has failed to re-examine the background of three-fourths of State Department workers with top-secret clearance - a violation of its own regulations, a congressional report showed Monday.

Some of the workers spared from re-examination in the last five years have committed serious security violations and crimes, but the State Department has no plans to reduce its testing backlog, the General Accounting Office said."As the espionage cases of the past few years have clearly demonstrated, U.S. government employees with security clearances and access to classified information are prime targets for recruitment," said House Government Operations Committee Chairman Jack Brooks, D-Texas, who requested the study.

According to the GAO, the investigative arm of Congress, more than 6,700 of the department's nearly 9,000 workers with top security clearance have not undergone a background check in the last five years.

More than 3,900 of those employees have not been investigated in more than 10 years, and dozens of workers have been spared from a re-examination in 25 years or more.

State Department spokesman Charles Redman refused to comment on the GAO report.

Potential employees at the department undergo extensive background checks before they are hired, but the government is required to conduct subsequent examinations at least every five years.

The study noted the department spends a large amount of money checking the background of job applicants, despite the fact that most of them are never hired.