Ed Miliband is to accuse David Cameron of pursuing a foreign policy of "isolationism" that has led to the "biggest loss of influence for our country in a generation" when he presents Labour's foreign policy in a speech today.
The Labour leader will also lay part of the blame for the refugee boat tragedies in the Mediterranean at the prime minister's door, saying Britain should have done more to plan for the aftermath of the fall of Muammar Gaddafi in Libya.
But, in the wide-ranging speech at Chatham House, he will also attempt to put some of his own party's ghosts to rest by insisting that he has learned the lessons of the Iraq war.
Miliband will set out the terms for military action under a Labour government and highlight the threats Britain is facing internationally, including from Islamic State.
In contrast to the Conservative promise of an in-out referendum on Britain's membership of the European Union, the Labour leader will also say he "will never put our national interest at risk by threatening to leave".
The Labour leader will say: "The Tory view threatens to weaken further our position abroad, a pessimistic isolationism that learns the wrong lessons from our past and undermines our nation's future.
"Or a Labour view that says we are stronger as a country when we look boldly, confidently outward to the world, not turning in on ourselves or acting on our own, but working with our allies, never for them: a genuine and hard-headed multilateralism with our values at its core."
Miliband will say that Britain has "more authority when we work" with global allies and will pledge to strengthen the UK's position in international institutions such as the United Nations, Nato, the Commonwealth and the European Union.
Leaving Europe would be profoundly damaging to the lives or our people and the future of our country.
The Labour leader will accuse David Cameron of presiding over the "biggest loss of influence for our country in a generation".
"That has happened because the government he led has stepped away from the world, rather than confidently towards it, sidelined in crucial international events time after time under this government, just at the moment when we needed to engage.
Underlining Labour's pro-European Union approach, he will say Britain's interests are being failed because other leaders "are reluctant to support us because they think we already have one foot out of the door".
"We will rebuild our influence and that starts with the European Union," he will add. "I want a clear message to be sent to our European partners that an incoming Labour government will be serious about leading once again in Europe and serious also about reforming Europe."