Blair told nearly 28,000 people who signed an on-line petition on his own website that ID cards would make an "important contribution" countering fraud, international crime and terrorism as well as tackling illegal immigration.
The petition - which calls for Blair to scrap the plan as it would not prevent terrorism or crime and would be "yet another tax on all law-abiding citizens" - is one of the most popular on the Number 10 Downing Street site.
Blair's e-mail to signatories said it would be "foolish" not to take the opportunity to use biometric data like fingerprints to secure a person's identity and disputed "exaggerated" claims about the cost of the scheme.
"Terrorists routinely use multiple identities - up to 50 at a time. Indeed this is an essential part of the way they operate and is specifically taught at Al-Qaeda training camps," he wrote.
"One in four criminals also uses a false identity. ID cards which contain biometric recognition details and which are linked to a National Identity Register will make this much more difficult." ...
"I recognise that these arguments will not convince those who oppose a National Identity Scheme on civil liberty grounds," he added...
The first ID cards are expected to be issued from 2008-09. Having one will be compulsory but citizens will not be required to carry them at all times. Such a scheme has not existed in Britain since World War II.
Campaigners such as the NO2ID group argue ID cards will erode civil liberties and that the scheme is based on untried, over-complicated technology used by an executive with unchecked powers.
They are also concerned at certain ethnic minority groups being unfairly targeted and the potential for it to be a "ready-made police-state tool" for any unscrupulous future government.
The main opposition Conservative Party and smaller Liberal Democrats are both opposed to the scheme.