Home Secretary Jacqui Smith has announced an extra 300 police jobs to target radicalisation.
She said it was not possible to "arrest our way out of the terrorist threat" and the aim was to stop people becoming terrorists in the first place.
Tories and Lib Dems questioned where the money and officers would come from.
The Tories also say the announcement was the "most blatant breach" of pre- election campaigning rules and have complained to the Cabinet Secretary.
They say an announcement of that sort should not be made in the three-week period before the local elections in England and Wales on 1 May.
'State of panic'
Shadow local government minister Eric Pickles told BBC Radio 4's The World at One: "This is the most blatant breach I've ever seen...
"All the sites likely to receive this additional personnel are up for election."
Mr Pickles added: "To use precious public resources in trying to bolster their [Labour's] poll position - we know they are in a state of panic."
Making her announcement, Ms Smith said the 300 new jobs included police officers and civilian staff and were in addition to funding for 400 officers to concentrate on disrupting terrorist plots.
The new roles would include training others, briefing on where radicalism might be happening, identifying people at risk of radicalisation, working with colleges, prisons and schools and building links with mosques.
In a speech she said they would work with communities and existing police: "We need to dissuade that very small minority of people who wish to harm our communities from becoming or supporting terrorists. That is the long-term challenge."
She told the BBC the jobs were being funded by money announced in last year's Comprehensive Spending Review, and said they were "additional jobs" over the next three years - funded in addition to money for "mainstream policing".
The Association of Chief Police Officers welcomed the announcement.
But Conservative security minister Dame Pauline Neville-Jones questioned whether the money was being "diverted" from other tasks and said the impact of the measures would be "limited".
It will increase the suspicion between local communities and the police. They don't want to see people being held for long periods
She said the government had a "weak" record on countering radicalisation - accusing it of delaying the prosecution of the radical cleric Abu Hamza al-Masri and of failing to ban groups like Hizb ut-Tahrir.
"We need long-term, concerted action across all of these areas and more direct involvement of moderate voices in British Muslim communities in the task of preventing radicalisation," she said. It comes as the government tries to win over MPs on plans to raise the limit on holding terror suspects without charge.
Liberal Democrat home affairs spokesman Chris Huhne said that "heavy-handed approach" ran "wholly counter" to Ms Smith's moves to improve the relationship between police and those at risk of turning to terrorism.
"There is also the question of whether this is actually new money, as it was previously announced as part of the Comprehensive Spending Review. It would be churlish to criticise it as a breach of election law," he added.
Inayat Bunglawala, from the Muslim Council of Great Britain, said feared moves to extend pre-charge detention would "completely undermine" the role of the 300 police officers and staff.
He told the BBC: "It will increase the suspicion between local communities and the police. They don't want to see people being held for long periods."
There is mounting speculation Gordon Brown could face his first serious Commons defeat as prime minister over the plans.
The Conservatives and Liberal Democrats oppose them and a number of Labour MPs have indicated they are unhappy with the plans.
Asked if it was the right time to pick a political fight, Ms Smith told BBC Radio 4's Today programme: "I'm not interested in a political fight, I'm interested in protecting this country from terrorism in the short term and in the long term."
Under the proposals, the home secretary could immediately extend the detention limit of a suspect from 28 to 42 days, if supported by a joint report by a chief constable and the director of public prosecutions.
The extension would then have to be approved by the Commons and the Lords within 30 days. But if either House voted against it, the power would end at midnight on the day of the debate.
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