WASHINGTON -- The multicolored terror alert system that was created after the Sept. 11, 2001, attacks could be getting an overhaul -- or could be eliminated entirely.

Homeland Security Secretary Janet Napolitano is expected to appoint a panel Tuesday to reevaluate the system, a senior administration official said.

The five-tiered system that goes from green, which signals a low danger of attack, to red, which signals a severe threat of attack, has proven to be confusing at times, and critics say the different colors are too vague to deliver enough information to be useful.

The official spoke on condition of anonymity because the announcement has not yet been made public. Homeland Security Department spokeswoman Amy Kudwa declined to comment.

Several members of Congress have expressed concerns about the current system. 

Sen. Joseph Lieberman, I-Conn., said that if the announcement is made, he supports the review. Lieberman, who chairs the Senate's Homeland Security and Governmental Affairs Committee, said Congress in 2007 required Homeland Security to improve the system and "provide greater specificity in its threat advisories and warnings," and include countermeasures as part of the program.

Those requirements have not all been met, and the calls for change have been bipartisan.

"Rather than rely solely on a color-coded designation, we wanted to make more information available to citizens, first responders and the private sector, so that appropriate steps could be taken by local officials and the general public," said Sen. Susan Collins, R-Maine, explaining Congress' reasoning behind the requirements added in 2007.

The system was widely panned from the outset. Democrats in particular criticized it in recent years, suggesting at times that the Bush administration was using the alert codes to swing public opinion by focusing attention on national security -- a signature issue then for the Republican White House.

The color-coded threat system was established by order of President George W. Bush in March 2002 as a way to inform law enforcement agencies quickly when intelligence indicated a change in the terrorist threat facing the nation.

It is made up of five colors designating increasing levels of risk of terrorist attacks: green, blue (guarded), yellow (elevated), orange (high) and red.

Currently, the alert level is at orange for the aviation sector, and yellow for the rest of the country. The nation has never been below yellow since 2001, although Hawaii put itself at blue for a year after the national system was adopted. It has since raised the level to yellow.

The United States hasn't been attacked since 2001, and the system hasn't changed since 2006 when a U.S.-bound terrorist plot was thwarted in Britain. At that time, the threat level for aviation was raised to red for flights from Britain.