The government is expected to back legislation to double the amount of time terror suspects can be held without charge.
It is thought that the Counter Terrorism Bill to be announced in the Queen's speech on Tuesday will include legislation to increase to 56 days the current 28-day limit.
Former prime minister Tony Blair suffered his first Commons defeat in 2005 after attempting to extend the limit to 90 days.
Home Office minister Tony McNulty said the government would be pushing for an extension "probably" of 56 days, while security minister Lord West said it would be "about 50".
McNulty told Sky News that people must understand that "14 days plus is extraordinary, 28 days plus is even more extraordinary, so there needs to be real substantial danger and circumstances" for the 56-day limit.
Lord Carlile, the independent reviewer of anti-terrorism legislation, said some suspects might need to be detained for longer than the current limit.
"There is a real risk that an extremely serious terrorism event could take place involving a large number of terrorists in which it would be difficult, if not beyond possible, to carry out all the necessary inquiries within a period of 28 days," he told BBC Radio 4's Today programme.
"If that eventuality is reasonably foreseen, and I foresee it, then in my view we should introduce a very highly protected system that would at least enable those most serious cases to be deal with properly.
"I think it's vital that nobody should be detained for an hour longer than is necessary. But also, nobody should be detained for an hour shorter than is necessary in the over all public interest, subject to the right legal protections."
In July, Gordon Brown pledged to consult on extending to a 56-day limit but insisted "we should not return to the previous [90 day] proposal rejected by the House".
And Lord West told the BBC that he had "no doubt whatsoever" that the limit proposed by Blair "was far too long".
"I think when it was tried to be done it was done in the most appalling way and we need to make sure we don't make that sort of mistake again," he said.
In some cases officials "really do need more time" to investigate, he said.
But he added: "We have to show absolutely that we really do need this and we have to show absolutely that we have real safeguards in place, certainly judicial oversight, Parliament would have to be told... and there may be other mechanisms we can do to look after people."
