Prime Minister Tony Blair on Wednesday proposed legislation to hold terrorism suspects for up to three months without charge as criticism mounted that he was overreacting to the July bombings in the London public transit system.

Blair, formally presenting his new terrorism bill to Parliament, said police had made an "absolutely compelling" case that they need to detain suspects for as long as 90 days without charge; the current limit is 14 days. Turning aside criticism that he was setting back civil rights, the prime minister declared that his job was to "protect people in this country and to make sure their safety and civil liberty to life come first."

Immediately after the July 7 bombings, in which four attackers killed 52 bus and subway passengers and themselves, Blair had strong cross-party support when he promised tougher measures to combat terrorism. But that support appears to be cracking as increasing numbers of politicians, Muslim leaders and human rights groups publicly criticize parts of the bill.

Charles Kennedy, leader of the Liberal Democrats, the number three national party, asked Blair on the floor of Parliament: "Why is it you remain so wedded to this proposal for 90 days? Surely it's wrong. Surely you are going to have to back down."

The proposal would also criminalize the "glorifying" or "encouraging" of terrorism in Britain or abroad. According to officials at a government briefing on the proposal, a person could be criminally charged for praising the Sept. 11, 2001, attacks in the United States or the London transit attacks, perhaps by calling the perpetrators "martyrs," if the intention were to encourage further attacks.

In addition, the bill would make it illegal to publish, disseminate or sell material that incites terrorism, giving authorities power to shut down bookstores and Web sites deemed to promote extremism. It would also become an offense to attend a "terrorist training camp," and the package would toughen penalties in existing laws and extend police investigative powers, including the three-month detentions.

Blair's proposals are dominating political discussion in a society that has long prided itself on guarding democratic principles and civil rights. Many analysts said Wednesday that the bill would probably be watered down before it became law, but they noted that Blair had broad public support for passing tougher anti-terrorism measures.

"A clear majority in principle is willing to sacrifice civil liberties to a certain degree in order to make Britain safer," said pollster Peter Kellner.

But hundreds of people, including Ken Livingstone, the mayor of London, turned out at a downtown hall Wednesday night to denounce the measure. Speaker after speaker called the proposals an affront to such cherished principles as free speech, trial by jury and the presumption of innocence.

Livingstone said the proposals brought back bad memories of the response to the start of the Irish Republican Army's violent campaign in 1969. He said the government passed emergency measures under which innocent people were locked up for long periods. Far from making Britain safer, he told the group Wednesday, this reaction helped the IRA recruit more members.

Shami Chakrabarti, director of the civil rights group Liberty, drew sustained applause when she said she feared that the new measures would largely target young Muslim men, who would be arrested, jailed for 90 days and then released with nothing more than an explanation that police had picked up the wrong "Mohammed Khan," a common name. She said such actions would play into terrorists' hands and urged Blair not to "give a blank check" to police.