The cross-party consensus on new anti-terror plans sends a signal to terrorists of "our unity to defeat them", Tony Blair has said.
Mr Howard wants phone-tap evidence used in courts
Mr Blair was speaking after talks with opposition leaders about introducing new laws, including bans on preparing, inciting or training for terrorism.
Tory leader Michael Howard said his call for phone-tap evidence to be used in courts was also being considered.
Lib Dem Charles Kennedy praised the government's "measured approach".
Other possible measures discussed included creating a specific offence of attending a terrorist training camp.
Mr Blair suggested there could also be a crackdown on bookshops selling publications which incited terrorism.
And the use of the internet to promote terrorism could be targeted.
Mr Blair has said he will consider allowing phone-tap evidence in court but that he will heed advice from the police and security services, who have previously opposed the idea.
Raising the time limit for detaining terror suspects without charge was also discussed at the meeting.
The Association of Chief Police Officers wants the limit increased from 14 days to three months. It argues more time is needed when dealing with complex terrorist operations.
'Hard to justify'
After the talks, Mr Blair said: "I think it perfectly reasonable for us in circumstances of great difficulty to have a greater detention in order that there can be the interrogation of people who are suspected of doing this."
Details about the length of detention and how judges were involved in the process would have to be considered, he said.
Mr Howard said a three-month limit would be "pretty difficult to justify".
He wants to know the number of cases where police believe 14 days of detention is not enough.
His concerns were echoed by Mr Kennedy, who said the limit had only relatively recently been raised from seven days.
But he suggested the new time limit could be tested or it could be raised to one month, not three, with extra scrutiny from judges.
The Lib Dem leader warned against legislating "in haste".
But Metropolitan Police Commissioner Sir Ian Blair later told Channel 4 News he and his colleagues did not want an automatic three-month detention period.
Instead, they wanted to be able to go to a judge after short periods to extend the detention in instalments - up to a three-month limit.
Detentions could be achieved in 14-day stints, he said, "each 14 days in itself complete, then we ask for another 14 days with judicial overview".
That would give more time to evaluate evidence already collected before pressing charges, he argued.
"Fourteen days does not allow for some of things we have to do in these kind of investigations - you've got encrypted computers, it takes a long time.
He said, for example, it had taken police a week just to enter the house in Leeds because of the risk from explosives.
"Fourteen days is a very short period of time to run one of these types of investigations."
But civil liberties campaigners stress that charging a suspect does not mean investigations cannot continue.