Jeremy Corbyn will say he is “not a pacifist” and accepts that military action is needed “as a last resort” at a speech in London on Friday.
But the Labour leader will say that is “very far” from the “almost routine” military interventions of recent times.
He will pledge a “robust”, independent foreign policy and “no hand holding” with US President Donald Trump.
The Tories said Mr Corbyn, long an opponent of nuclear weapons, had “spent a lifetime trying to disarm Britain”.
In a speech to the Chatham House international affairs think tank on Friday, Mr Corbyn will say he will do “everything necessary to protect the safety and security of our people and our country”, should his party win power on 8 June.
The Labour leader, a former chairman of the Stop the War Coalition who has criticised British and US military interventions in Syria, Iraq and Afghanistan, will say the UK’s interests are best served by pursuing peace.
“But I am not a pacifist. I accept that military action, under international law and as a genuine last resort, is in some circumstances necessary. But that is very far from the kind of unilateral wars and interventions that have almost become routine in recent times.”
He will say a “bomb first, talk later” approach to security “has failed” and is a “recipe for increasing, not reducing threats and insecurity”.
“Waiting to see which way the wind blows in Washington isn’t strong leadership. And pandering to an erratic Trump administration will not deliver stability,” he will say.
“Britain deserves better than simply outsourcing our country’s security and prosperity to the whims of the Trump White House.
“So no more hand holding with Donald Trump – a Labour government will conduct a robust and independent foreign policy made in London.”
A leaked draft version of Labour’s manifesto on Wednesday suggested the party would support the renewal of the Trident nuclear submarine system, commit to the Nato benchmark of spending at least 2% of GDP on defence and would work with international partners and the UN on multilateral disarmament.
But the Conservative armed forces minister, Mike Penning, said: “Jeremy Corbyn has spent a lifetime trying to disarm Britain but now he’s pretending he’s got what it takes to keep us safe.
“It’s nonsense – we know he wants to scrap Trident, abandon our allies and would rather talk to Daesh [so-called Islamic State] than strike its barbaric leader.”