The change in airport security profiling comes after a three-month review ordered by President Barack Obama, and amidst fears and complaints that racial profiling could affect 675 million people - both American Muslims and travelers from the Middle East.

Washington's announcement will replace mandatory enhanced screening of all passengers traveling to the United States from 14 mostly-Muslim nations, including Saudi Arabia, Pakistan, Afghanistan and Yemen which were put into place following a failed Al-Qaeda attempt to blow up a Detroit-bound flight on Christmas Day.

The new measures to begin this month involve travelers' personal characteristics matching intelligence on potential attackers.

Officials said the new measures, which will come into force beginning this month, will "significantly" reduce the number of passengers chosen for mandatory extra screening, eliminating entire swaths of travelers who had been chosen based on their nationalities.

But it will also broaden the number of potential targets for secondary searches, expanding the focus from the 14 named countries to dubious passengers from anywhere in the world, a move also designed to outsmart terrorist plotters who know which countries are affected.

The level of screening of travelers will depend on how closely their personal characteristics match against intelligence on potential terrorists and will take into account characteristics like nationality, age, recently visited countries, and partial names.

This means that even US citizens traveling back home will be subject to special screening if they match certain profiles.

The US government currently has a 6,000-name "no fly" list of suspected terrorists, who are banned from flights to or within US territory.

And, while the US does not have the authority to screen passengers in foreign airports, it can sanction air carriers if they do not agree to follow US guidelines for international aviation security.

Muslim advocacy groups, meanwhile, say an increasing number of Muslim and Arab US citizens and permanent residents who travel abroad have faced complications in returning to the US because of heightened security.

About two-thirds of the estimated 2.5 million Muslim Americans were born abroad, according to a 2007 survey by the Pew Research Center, and they travel frequently to their native countries.

In that same survey, 53 percent said it was more difficult to be a Muslim since the Sept. 11 terrorist attacks. Most also believed the US government "singles out" Muslims for increased surveillance and monitoring.

Khalilah Sabra, director of the immigrant justice program at the Falls Church-based Muslim American Society, said that since Christmas the organization has seen a 50 percent increase in reports of extensive questioning and delays of Arabs and Muslims, to about 16 cases a month.

"Getting out (of the US) is OK. No one says anything, but when they try to come back they are not allowed in, or they are being questioned," she told reporters.

"It's really having a chilling effect," Ibrahim Hooper, a spokesman for the Council on American Islamic Relations, told reporters.  "People do whatever they can now not to cross borders if they're Muslim because they feel there's some potential for humiliation."

The State and Homeland Security officials have acknowledged that the lists can produce false positives. And people are never told whether they were on a list or removed from one; the only way to know is to try flying again.