Sir Menzies Campbell has hit out at "idle chatter" from within his party about his performance.
Sir Menzies insists he will lead Lib Dems into the next general election
The Liberal Democrat leader used a speech to grassroots supporters to restate his vow to lead the party into the next general election.
He downplayed a warning by Lib Dem president Simon Hughes that he must raise his game, declaring: "We must all raise our game."
Sir Menzies also denied his party was being squeezed out by the Tories.
He told the BBC: "The Liberal Democrats are well known for their willingness to express themselves - nothing new. What I do is get on with the job. That's the most important thing to do."
Asked for his message for Mr Hughes, he replied: "Message to every Liberal Democrat: we must all raise our game.
"We must all ensure that the free fair and green society which is essential for the future of the people of Great Britain lies right at the very top of our political agenda on every possible occasion."
But his fightback came as a poll found half of Liberal Democrat voters in crucial marginal seats believe Gordon Brown or David Cameron would make a better prime minister.
A survey for The Daily Telegraph across 112 marginal seats held by Labour and the Lib Dems suggests only a quarter of those who intend to vote for his party would want him in Number 10.
Addressing his party's eastern region conference in Suffolk, Sir Menzies said: "I want to tell you that I have the energy, the ideas and the determination to lead this party into the next general election and beyond.
"We will campaign on the issues that matter to people - climate change, council tax, tuition fees and free long-term care for the elderly, and Iraq.
"These are things that matter to people - not the idle chatter of the occasional dissident."
He insisted the Lib Dems were making progress in by-elections, adding: "They tell us that David Cameron's Conservatives are on the march. But I say that here in the east of England we are able to show otherwise."
Mr Hughes, who fought Sir Menzies in the last leadership contest, told GMTV: "The leader obviously has to do better, get better at getting the message across better, at getting the policy out better."
The Lib Dems' conference in Brighton was overshadowed by speculation about possible leadership bids by environment spokesman Chris Huhne and home affairs spokesman Nick Clegg.
Both have ruled out standing against their leader but the PM's decision not to hold an early election has led to fresh conjecture that Sir Menzies will face a challenge.