As Carol L. Friedland listened to the hissing sound that issued from her radio on Sept. 11, she waited patiently for an urgent message from the nation's Emergency Alert System.

She had tuned to news coverage on WNYC-AM in Manhattan shortly after the terrorist attack on the World Trade Center, when the station abruptly went silent with the collapse of the north tower and the destruction of its transmitters. Still, she waited.

After all, through the decades, she had listened to such an abundance of alert announcements that she could recite them by heart: ''This is a test of the emergency broadcast system. The broadcasters in your area, in voluntary cooperation with federal, state and local authorities, have developed this system to keep you informed in the event of an emergency. For the next 60 seconds, you will hear a tone that will be used to alert you in case of an actual emergency. Remember, this is only a test.''

But the alert never came.

''Planes were hijacked,'' said Dr. Friedland, a Manhattan psychologist who spent the rest of that day counseling traumatized New Yorkers who escaped from the disaster. ''America was attacked. If this was not 'an actual emergency,' then what is? Where was the Emergency Alert System?''