The State Department has extended the time many foreign students and scientists can remain in the country before renewing security clearances in response to concerns that strict visa requirements are discouraging them from coming to the United States.

The clearance is required for foreigners working in areas the government deems sensitive, including fields like chemistry, engineering and pharmacology. The change will lengthen the validity of the clearance to up to four years for students, two for working scientists, making it easier to remain in the United States for the duration of work or study programs. Until now, they had to reapply for clearance each year. The State Department consulted with the Department of Homeland Security before granting the extension.

The security clearance program, known as Visas Mantis, was established in 1998 to prevent scientists from illegally transferring technology out of the country. After the Sept. 11 attacks, the caseload increased and the process became more time-consuming. Several of those who carried out the Sept. 11 hijackings had been issued student visas.

A study released last February by the Government Accountability Office found that scientists had been waiting an average of 67 days for a decision on their Visas Mantis clearances. The office is to release a follow-up report on Friday at the annual meeting of the American Association for the Advancement of Science.

The State Department has taken other steps to expedite Visas Mantis security clearance, including investing $1 million in technology upgrades. The agency estimates that the extension will reduce by 50 percent the number of Visas Mantis clearances to be handled each year.