WASHINGTON (AP) _ The Federal Aviation Administration on Friday warned pilots that they could be forced to land _ or even shot down _ if they enter restricted airspace.

The FAA also allowed some news helicopters and blimps back in the skies, but not near 28 major urban centers.

The agency's notice to pilots said that, as a last resort, they could be shot down by military planes if they enter restricted airspace. Before the Sept. 11 terrorist attacks, pilots who flew into off-limits areas first faced a warning from air traffic control and then would be fined or could lose their license.

But the FAA on Friday told pilots that they would be intercepted by military aircraft in such circumstances.

Pentagon officials said earlier this week that two Air Force generals now have been the authority to order the military to shoot down any plane threatening a U.S. city. Dozens of American cities are being patrolled by F-15s and F-16s.

Restricted areas are closed to civil aviation, including passenger jets and private planes.

All U.S.-registered pilots are getting a letter from FAA Administrator Jane Garvey telling them of the new procedures, the agency said.

The FAA also announced Friday that news helicopters and blimps would be allowed back in the skies in most areas _ although not around 28 urban areas, including New York, Washington and Los Angeles.

The FAA's ban on flying near stadiums continues. Within a 3.4-mile radius of a stadium, planes cannot come closer than 3,000 feet above the ground. The only exception is if an air traffic controller allows an arriving or departing plane to come closer; Shea Stadium in New York City is in the flight path for nearby LaGuardia Airport.