Charles Kennedy set out his party's stall for the Euro election campaign by going on the offensive over Iraq.
The campaign will be a test for Kennedy after health worries
The Lib Dem leader hopes to capitalise on his party's opposition to the US-led invasion.
He said voters felt their views had been ignored by the government and the euro poll was the "most appropriate forum" to send a message to Tony Blair.
The Lib Dems also called for a "more accountable, more democratic" Europe as they launched their campaign.
The elections will be seen in some quarters as a test for Mr Kennedy's leadership following rumours in March about his health when a stomach bug forced him to miss the Budget debate.
But the Lib Dem leader told BBC Radio 4's World At One he had been "on the road" campaigning for most of the last month and had a "spring in his step".
He denied his party was being opportunistic in campaigning on Iraq when the European Parliament could not change British policy on the issue.
Instead, he argued that European Union institutions needed to adopt a more coherent approach to international affairs.
Voters were clearly very anxious about the Iraq situation, said Mr Kennedy.
"They are also increasingly alarmed by the fact that Britain appears to be being led by the nose by this present American administration," he said.
"Many of them are saying to themselves: 'Well, on balance on this issue we would have preferred to have stayed closer to our European allies rather than find ourselves increasingly isolated with George Bush.'"
The Lib Dems are branding George Galloway's Respect coalition - also chasing the anti-war vote on 10 June - as "decided also-rans and rather irrelevant to this election".
With the slogan "Making Europe work for you" the Lib Dems also sought to portray themselves as a "Euro-reform" party.
Charles Kennedy may be frustrated that his consistent scepticism over the war on Iraq appears not to have translated into popular support for his party
Mr Kennedy denied that stance was a reaction to public scepticism about the way the EU worked.
But party chairman Matthew Taylor earlier admitted the party had not been loud enough "in the past" in its calls for a more accountable and democratic Europe.
The environment is another key plank of the Lib Dem platform, with the party arguing that closer cooperation in Europe could help tackle issues like pollution.
The new manifesto says the EU should be at the forefront of talks to persuade other countries to ratify the Kyoto treaty on climate change.
The Lib Dems are looking to improve on their 1999 European election showing, when they received 12.7% of the British vote and won 10 European Parliamentary seats.
Their tally of MEPs rose to 11 in November 2000 when Bill Newton Dunn defected from the Conservatives and the Lib Dems say they are confident they can make more gains than their rivals in June.
The party will launch its local election campaign next week.
Last week the Conservatives launched their European election campaign last week, saying they did not "want to be part of a country called Europe".
Labour has yet to launch their European campaign but for the local polls are warning voters not to let the Tories "wreck it again" and pointing to their record on the economy.
The Green Party and UK Independence Party also have their European manifesto launches coming up, although UKIP is already using posters pushing its call for Britain to withdraw from Europe.