Tony Blair has said he still wants to give police controversial new detention powers - despite facing stiff opposition in the House of Commons.
Home Secretary Charles Clarke on Wednesday headed off a possible defeat on plans to allow terror suspects to be held for up to 90 days without charge.
But Mr Blair said police had asked for the powers and should get them.
"This is not an issue to play around with," he said, accusing critics of putting terror suspects' rights first.
"The civil liberties of the majority who need protection should come first," the prime minister told BBC News.
As the government's troubles on the anti-terror plans continued, the home secretary admitted he had been wrong to tell MPs the attorney general had personally ruled the proposals would not break human rights laws.
Mr Blair said police and those heading anti-terror operations wanted the current detention time limit of 14 days raised to 90 days because of the complexity of terrorism cases.
There had to be a "very good reason" for politicians to say "no, we know better than you", he argued.
On Thursday Mr Clarke told MPs there was no consensus for the 90-day proposal.
A backbench attempt to force through a compromise time limit of 28 days was withdrawn when Mr Clarke promised to return with new plans next week.
But Mr Blair warned: "If we are forced to compromise because we can't get the legislation through, then nobody should be in any doubt: that is not the right solution.
"The best solution is to do what the police say they need in order to protect the country from terrorism."
Former Cabinet Minister Frank Dobson, told BBC Radio Five Live Mr Blair should "back off" if he wanted to avoid defeat in Parliament.
He said: "We now understand that the prime minister has told the Cabinet that he wants it to stay at 90 days.
"Well I wouldn't like to be responsible for trying to manage the Parliamentary Labour Party if we're left in a position where we can't believe a word the home secretary says."
Mr Blair saw his closest parliamentary majority ever on a different part of the terror laws on Thursday.
BBC political editor Nick Robinson said some MPs believed Mr Blair was trying to talk tough while preparing for a climbdown over the detention debate.
Question of authority?
Earlier, outgoing Conservative leader Michael Howard said he wanted to reach agreement - but said the current plans did not "withstand scrutiny".
Mr Blair on Wednesday suffered a double blow of the troubles for the terror plans and the resignation of David Blunkett.
"What we saw yesterday was the authority of the prime minister diminishing to vanishing point," said Mr Howard.
Liberal Democrat leader Charles Kennedy has said his party will oppose any extension of the current 14 day detention time limit.
But the prime minister dodged questions about whether his authority was damaged and said critics should talk to their communities about the issue before next week's votes.
As debate continued in Parliament on the Terrorism Bill, the home secretary apologised to MPs over what he said on Wednesday about the attorney general's opinion.
The attorney general, Lord Goldsmith, is the government's senior law officer and Mr Clarke's comments have fuelled calls for his legal advice on the terror plans to be published.
Newspaper reports have suggested Lord Goldsmith is very concerned about parts of the plans.
On Wednesday Mr Clarke said Lord Goldsmith had personally told him the plans were in line with the European Convention on Human Rights.
A day later, he said: "I should clarify that the clear legal advice I received as to the bill's ECHR compliance... did not come from the Attorney personally."
Mr Clarke also apologised for breaking the long-standing convention that the advice of government law officers should not be made public.