WASHINGTON -- The government has tightened its immigration policies, promising to use more extensive background checks and better intelligence-sharing to keep out suspected terrorists and their supporters.

Attorney General John Ashcroft has asked the State Department to designate terrorist organizations whose members or supporters will not be permitted to enter the country.

Ashcroft said he was creating a foreign terrorist tracking task force to promote better coordination between intelligence, law enforcement and immigration officials.

He promised that the government will conduct more extensive background checks on people seeking visitor visas and will turn the information over to the CIA and FBI for further investigation before issuing permission to enter.

``This is clear authority that strengthens our ability to say to terrorists, you're not welcome in the United States,'' Ashcroft said.

The sudden tightening of immigration policies came amid growing criticism contending terrorists can enter the country too easily, including people who enter the U.S. with student visas and are not tracked after they enter.

The new foreign terrorist tracking task force will be charged with denying entry to members or representatives of terrorist organizations and immigrants who are suspected of having engaged in or provided support for terrorist activities.

Ashcroft said the new immigration task force will be headed by Steven C. McCraw, the deputy assistant director of the intelligence branch of the FBI's Investigative Services Division.

Immigration Commissioner James Ziglar said the task force will provide immigration officials with ``real time access to information'' that will allow them to keep suspected terrorists out of the country.

``We're not talking about immigration,'' he said. ``We're talking about evil.''