Lady Scotland told the House of Lords that she understood some peers hoped to table an amendment supporting the measure, despite its dramatic defeat in the Commons earlier this month.

The terrorism bill will extend detention from 14 to 28 days instead, after 49 Labour rebels voted with Tories and Liberal Democrats in Tony Blair's first defeat in a vote as prime minister.

Opening the legislation's second reading in the upper chamber, the minister said that the government still believed that 90 days was appropriate, but would not back any amendment to that effect. The home secretary, Charles Clarke, had already said that the government would not seek to overturn the Commons decision.

Lady Scotland added: "No one can doubt the threat from international terrorism. The challenge to us is to devise a legislative programme which meets that threat whilst safeguarding rights. We believe this bill meets that challenge."

But Tories and Lib Dems warned that they would introduce amendments scrapping the glorification clauses when the legislation reached committee stage. An opposition amendment in the Commons was defeated by just one vote.

"We shall seek to remove the glory glory hallelujah sections from the bill," said the Lib Dem peer Lord Thomas of Gresford, warning that the wording of the clauses was emotive and could be understood differently by different people.

Lord Hurd, the Tory former home and foreign secretary, added: "We need not to worry so much about the loudmouths as about the quiet acts of subversion and training by dangerous people, up and down the country, who on the whole keep their mouths shut."

But Lady Symons, a former Labour Foreign Office minister, said that the nature of terrorism had changed. "Today's terrorism is less organisation-based and more movement-based than in the past.

"This type of terrorism peddles its special brand of hatred through direct incitement and encouragement, mainly of young people, to emulate those who are held up as martyrs."

Lady Ramsay, another Labour peer, stressed that the government had already made substantial alterations to the bill, including narrowing the definition of glorification.

Lord Carlile, the anti-terror legislation watchdog, used the debate to call on the public and other politicians to help him examine the definition of terrorism. He has undertaken a year-long review at the request of the government, following widespread concern in the Commons that the eight-line description is too vague.

The Lib Dem peer said that he had found himself on all sides of the argument about the bill, adding that while Britain faced a continuing terrorist threat its response should be proportionate.

"I would urge this house and the other place to take a carefully balanced view of the bill. This is not an abstract issue," he warned.

At present, aspects of the bill appeared to make it illegal for academic experts on terrorism to carry out their research, he added.

Lord McNally, leader of the Lib Dem peers, urged colleagues to consider whether powers given in the six terror-related bills seen by parliament since 1997 had been used properly effectively.

"Otherwise every terrorist outrage will bring forth another bill, another notch on the ratchet, another turn of the screw until we find ourselves without the civil liberties which we are fighting terrorism to defend," he said.