Plans to extend the period that terror suspects can be held without charge will not be forced through without cross-party agreement, says John Reid.
Mr Reid said the Home Office had to change
The Home Secretary told the Commons Home Affairs Committee he wanted consensus on the controversial plans.
Mr Reid also defended the decision to split up the Home Office - dividing responsibility for counter terrorism from that for probation and prisons.
He told MPs that "as the world changes, we have to change our response".
Government attempts to extend the 28-day limit on holding terrorism suspects without charge to 90 days failed in 2005, opposed by Tories, Lib Dems and some Labour MPs.
Police say gathering evidence from computer hard-drives, mobile phone records and various fake identities means they need more time.
On Tuesday Mr Reid emphasised that he wanted cross-party agreement on the issue, telling MPs: "Wherever possible I want to try and reach a national consensus on national security.
"And if on that issue it proves that, notwithstanding the experience of the past year, that there's no such national consensus on that issue, then I will not proceed with it."
But he added: "I do feel that I have an obligation, as the minister in charge of the police, when they think it merits discussion, to bring it and discuss it with colleagues inside and outside of government."
Later, shadow home secretary David Davis said 28 days was the longest period in the western world of detention without trial.
He said it should not be extended unless there was clear evidence that it would improve national security.
"The Attorney General made clear last week that no such evidence exists, and our discussions with police officers have found no such evidence either," he said.
Mr Reid also defended plans to split the Home Office - the Department for Constitutional Affairs is due to become the Ministry of Justice and take over probation and prisons from the Home Office.
Alarm at changes
Earlier, former Lord Chief Justice Lord Woolf said changes at the Home Office were happening too quickly, and without sufficient consultation.
Mr Reid told MPs: "As I understand it...he is saying this can be made to work but we want to talk about how we make safeguards on it.
"I think he said the main thing was to protect the wellbeing of the nation. I entirely agree with that. That is what is behind all these moves."
On Tuesday, committee chairman John Denham asked him why it had become necessary to give away what, for 150 years, had been a defining part of the Home Secretary's job.
Mr Reid replied: "I think the main responsibility of government is the protection of life and liberty of our citizens and they are under threat from terrorism as never before."
Meanwhile, an Office for Security and Counter Terrorism will be set up within the Home Office, which will start advertising for someone to head it up on Wednesday.
MPs were told that the new director general could be in place within seven weeks.