WASHINGTON?President Bush moved to tighten restrictions on foreign student visas Monday, part of an effort to bar the entry of immigrants who commit or support terrorism.

Bush was directing top aides to study the foreign student visa system and develop recommendations for tighter controls, a White House official said.

Several of the 19 hijackers who crashed planes on Sept. 11 entered the United States legally with the kinds of visas routinely granted each year to thousands of foreign students.

Some lawmakers have proposed a six-month moratorium on new foreign student visas until a system for tracking them can be implemented. Bush was stopping short of that step Monday, an aide said.

Bush also planned to announce creation of a foreign terrorist tracking force that would coordinate efforts by government agencies to keep those with links to terror organizations out of the country, said White House spokesman Ari Fleischer.