The government should not let the public mood dictate legislation in the wake of the 7 July London bombings, Lib Dem leader Charles Kennedy has warned.
He criticised Tony Blair's plans to extend powers to deport or bar from the UK foreigners who encourage terrorism.
Mr Kennedy said the Lib Dems may not support the legislation, which could threaten the cross-party consensus which has been in place since 7 July.
But Lord Chancellor Lord Falconer said the move could prevent future attacks.
"If you are saying things that encourage people to become suicide bombers, that should be against the law," he said.
"It is not against the law at the moment, that's why we need more legislation for it."
He also told BBC News it was vital that the country remained united behind the prime minister.
"It is so important that there is unity, not just across the political consensus... but also in the Muslim community as well," he said.
Conservative leader Michael Howard said his party has been calling for the measures for years and, in principle, backed them.
"It is important a united front is maintained in the face of the terror threat, " he said.
But Charles Kennedy said while he wanted to preserve the consensus, he was concerned that the Lib Dems had not been given notice of some of the measures which were outlined on Friday.
Home secretary to consider deporting any foreigner involved in listed extremist centres and websites
Make justifying or glorifying terrorism anywhere an offence
Automatically refuse asylum to anyone with anything to do with terrorism
Examine calls for police to be able to hold terror suspects for longer before pressing charges
Use more control orders against British terror suspects
Create a list of preachers who will be kept out of the UK
"There is a worried mood in the country, and rightly so, about the problems and dangers being faced and the terrible events that have taken place.
"But you can't just legislate by mood. You have also got to legislate introducing means which actually set out what you are trying to achieve.
"If you have an international war on terror, does it make sense simply to re-export a source of potential terror from your own country, rather than dealing with that individual and that issue within your own jurisdiction so that you have some control over it?"
The measures have been welcomed by Metropolitan Police Commissioner Sir Ian Blair, who said he was "very pleased" with the plans and that they fulfilled most of the requests for new powers made to the prime minister by police last week.
They have already identified people they want to target under proposed new anti-terrorism measures, he added.
The UK can already exclude or deport those who pose a threat to security, but the prime minister said on Friday he also wanted to clamp down on those who advocated terror.
One of the measures will make it an offence to "justify or glorify terrorism" while people would be refused asylum if they had been involved in terrorism.
The prime minister unveiled the anti-terrorism proposals on Friday, at his final news conference before his summer break.