Charles Kennedy has closed a conference overshadowed by tragedy with the words of former US president Roosevelt, calling on party members to realise their dreams of becoming a major force in British politics.

In an emotional 35-minute speech, the leader of the Liberal Democrats used Roosevelt's words to rally his grassroots supporters.

"The only limit to our realisation of tomorrow will be our doubts today. Let us move forward with strong and active faith. By overcoming our doubts and fears of today, and by working with our friends, we will indeed realise our dreams tomorrow," he said.

Kennedy devoted more than half of his 35-minute speech to the international crisis and his advisers had admitted they had been "on standby" to tear up his script and start again at any moment.

Urging caution in Britain's response to the tragic events in America, Kennedy warned Tony Blair to avoid associating himself with the hawks. In a clear attempt to put distance between himself and Tory leader Iain Duncan Smith, he told the conference: "We do a disservice to democracy itself, if we meet terror with terror."

He called for a greater role for the UN, Nato and the EU in the current military operations. Kennedy added that the events of September 11 showed the Eurosceptics that isolation could never work.

He also told the party faithful that they had to "engage" more with Tories who felt the Conservative party under Iain Duncan Smith was no longer their natural home. "When they come to us they will be guaranteed a very warm welcome indeed."