The change will cost private companies and agencies millions in revamping of existing security measures, web sites, alerting systems, continuity and emergency plans which are keyed around the current system.

The nation's color-coded terror warning system will be phased out beginning this week, over the next 90 days according to government officials familiar with the plan.

The officials requested anonymity to speak ahead of an announcement scheduled Thursday by Homeland Security Secretary Janet Napolitano.