The U.S. Department of Homeland Security has released a revised plan for phasing in a national identification card program that was set to begin this year.

The department has extended deadlines and made other changes to address the concerns of states about the cost and timeframe for compliance.

Passed by the U.S. Congress in 2005, the Real ID Act establishes national standards for driver's licenses and other state-issued identification cards. The aim is to make it harder for terrorists, illegal immigrants and others to obtain or counterfeit identity documents.

At a news conference Friday in Washington, Homeland Security Secretary Michael Chertoff said the phased-in program gives states greater flexibility in implementing it.

Under the new timetable, people under the age of 50 must be issued Real ID - compliant identification cards by the end of 2014. For people over 50, enrollment may be extended to the end of 2017.

The new ID cards will be needed for boarding a plane or entering a federal building.

The original program was rejected by 17 states in part because it was expensive. But the cost of the new plan has been reduced by more than 70 percent - from $14.6 billion to $3.9 billion. Chertoff estimates it will cost states about eight dollars to make a Real ID license.

Lawmakers called for stricter identification requirements after the September 11, 2001 terrorist attacks. The Department of Homeland Security points out that the hijackers in those attacks obtained 30 drivers licenses and used 364 aliases.

But critics argue the ID program could put at risk the privacy of citizens, saying it creates a database of personal information that could be hacked into or otherwise compromised.

Some information for this report provided by AP and Reuters.