The U.S. government is changing visa procedures to make it easier for some foreign students wishing to study science or other technical fields in the United States.

The changes are intended to speed up the process of approving security clearances and allowing those clearances to remain in effect longer.

U.S. officials have struggled to balance competing goals of inviting foreign scholars, who provide an intellectual and financial boon to many American universities, while preventing sensitive technology from being illegally transferred out of the country.

Asa Hutchinson (search), the department of Homeland Security's under secretary for border and transportation security, said U.S. officials "are now better able to accommodate researchers and students who lawfully enter our country."

"This change sends a clear message that the U.S. highly encourages those with great scientific minds to explore studying and working in our country," he said in a statement.

The changes affect the security clearance known as Visa Mantis (search), established in 1998. These clearances are separate from the visa procedures and sometimes have expired while students were in the middle of their studies, requiring them to submit new applications.

Under procedures outlined by Homeland Security (search) and the State Department, international students will be able to keep their clearances for the duration of their academic programs, up to four years. New clearances would be needed for students who change their field of studies.

Clearances will be approved for up to two years for temporary workers and exchange visitors and for one year for business visitors and visitors for pleasure.

The State Department said it has reduced the average time for receiving security clearances to under 14 days. A study by Congress' Government Accountability Office found that the average time for approval was 67 days between April and June 2003.