He said there should be no limit on the development of the database because it was vital for catching serious criminals.
The Conservatives accused him of attempting to expand the DNA database by stealth and called for Parliament to vote on whether details of people who were innocent or not charged should be included against their wishes.
The Prime Minister said the public backed the extended use of DNA and urged police forces across the country to make use of technological advances to reopen thousands of unresolved "cold cases".
During a tour of the Forensic Science Service headquarters in London, he dismissed concerns of opposition politicians, saying the public backed the database because it was "helping us track down murderers, rapists".
The national DNA database has expanded by about a third to 3.6 million profiles since the Criminal Justice Act 2003, which allowed police to take and keep DNA samples from everyone arrested for any imprisonable offence - regardless of whether they were eventually convicted.
Mr Blair voluntarily gave a DNA sample in 1999 when he announced plans to build up the database.
Asked whether there should be any restrictions on the number of people included, Mr Blair said: "The number on the database should be the maximum number you can get."
Mr Blair said he did not believe there was "any problem" with the public providing samples because if they had committed a serious offence they "should be convicted". The database sent a "strong signal" to the criminal community that they could be identified and caught from even the smallest trace at a crime scene.
Downing Street said later that no thought had been given at this stage to requiring everyone to give a DNA sample, although they will have to give scans of their eye and fingerprints for a passport and eventually a national identity card. At this stage, the Prime Minister believed it was a "personal matter" whether people, including other Government ministers, should volunteer their DNA.
Mr Blair visited the laboratories to highlight success in solving about 100 harrowing cases, including rapes and murders dating back as far as 20 years. Advances in the technology mean that old samples from scenes can be re-analysed and matched against profiles on the database in "cold case" reviews.
This enables the reopening of cases not because of new evidence, but due to new forensic techniques. The project has so far resulted in 21 convictions, with several other suspects arrested and awaiting trial. Government sources say the majority of the active criminal population now have their DNA recorded. Police receive more than 3,500 DNA matches a month, double the figure in 1998/99.
The Criminal Justice and Police Act 2001 permitted police to retain DNA samples from everyone who was charged. Previously they had to destroy samples and fingerprints from anyone who was found not guilty or had their charge dropped.
The Criminal Justice Act 2003 gave police the power to take and keep a DNA sample.
The use of the new powers has proved controversial. Earlier this month, The Daily Telegraph reported that a grandmother who was arrested after a dispute with a neighbour was required to give a DNA sample. The case was later dropped for lack of evidence but her DNA will remain on the database.
The UK has the largest database in the world and is drawing attention from countries throughout Europe keen to learn from its experience.
Damian Green, the Conservative's home affairs spokesman, accused Mr Blair of making "policy on the hoof" without thinking through the implications.
The DNA database could be a vital tool in the fight against crime but the terms of its use must be properly laid down and approved by Parliament.
"There is no provision to deal with people who have a DNA sample taken, are innocent of any crime but still remain on the database," said Mr Green.
http://www.telegraph.co.uk/news/uknews/1532210/DNA-database-should-include-all.html
