Gordon Brown declared that protecting the country from terrorism would be his "first priority" as Prime Minister, dismissing Tory calls for a dedicated cabinet security minister.
The Chancellor - the overwhelming favourite to succeed Tony Blair in Number 10 - said it was for a PM to "take the lead" and for the rest of the ministerial team to "play their part".
Mr Brown, in an interview with the Sunday Times, also backed calls earlier in the day from Britain's top police officer Sir Ian Blair for anti-terror powers to be toughened.
Tory leader David Cameron, writing in the same newspaper, reiterated his pledge to have a full-time terrorism minister alongside the Home Secretary in his cabinet should he win power.
"Action against terrorism deserves a dedicated seat at the top table," he said. However the Chancellor dismissed the idea, saying: "Every minister and every agency of government must take responsibility for security - each of them must play their part.
"But ultimately, because the fight against terrorism must be fought both at home and abroad, it is the Prime Minister who must take the lead, as Tony Blair has done. If you are prime minister, you cannot devolve responsibility for protecting the nation. It must always be your first priority."
The Chancellor said he "completely agreed" with Sir Ian's calls for stronger powers - including extending the 28-day limit for holding terror suspects without charge.
The Metropolitan Police Commissioner used a speech in Berlin to demand a swift rethink, warning that if there had been more than 24 suspects in the recent alleged airline plot "we would probably have run out of time".
Sir Ian also used his speech to call for a shake-up of the way courts deal with terror trials, warning the system was "creaking under the impact".
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The police chief's address followed Friday's bleak warning from the head of MI5 Eliza Manningham-Buller about the scale of the al Qaida threat. She said terror network was mounting a "sustained campaign" against Britain and that the threat was "growing" and would "be with us for a generation".
