John Hutton has become the first defence secretary to back a French plan for a European army, branding those who dismiss it as “pathetic”.

In a wide-ranging interview with The Sunday Times, he said: “I think we’ve got to be pragmatic about those things. Where it can help, we should be part of it.”

His support goes beyond the public position of Gordon Brown, the prime minister, and will antagonise those who believe that further European cooperation will undermine Nato by excluding the United States.

Nicolas Sarkozy, the French president, has sought to develop Europe’s military structures with new headquarters and rapid reaction forces, each consisting of 1,500 troops from member countries.

Hutton said: “France is one of our closest allies, militarily. The French believe very strongly in this type of role. If we can support it, we should.”

He added that working with EU allies on military missions was “perfectly sensible.” He emphasised that Britain should not contribute troops to joint EU operations if it risked compromising other missions, and cited plans for a European Union-led mission to tackle piracy off Somalia as a “good example” of how such forces could be used.

“I’m not one of those EU haters [who think] anything to do with the EU must by definition be terrible. There’s plenty of them around. I think frankly those kind of views are pathetic,” he said.

“Britain’s role in the world is to be part of those alliances – that’s the best way to project power, strength and conviction around the world. People who don’t understand that don’t understand the nature of the modern world.”

Liam Fox, the shadow defence secretary, said strengthening the EU’s military identity could undermine Nato: “What we must not have at a time of scarce resources is duplication of existing structures and diversion of capabilities away from Nato’s use.”

Hutton, who was giving his first interview as defence secretary since his appointment earlier this month, also said: British troops are likely to be in Afghanistan for decades. The Afghan mission will fail unless there is a new “focus”. A big defence procurement project must be cut. People who jeer at returning servicemen are “cretins”.

In a frank assessment of the pressures on the services, he also admitted that the military is breaking its own guidelines over periods of rest for troops between operational tours because it is so stretched: “It’s not how it should be.”

On Afghanistan, he said: “It will be a long campaign: we’ve got to be honest with people about that. There’s no quick fix.” He said it would take years to crush the Taliban and “could well” take decades to achieve the allies’ wider objectives.

Hutton said it would be “pointless” to deny that Britain’s resources were under intense pressure, with specialised units such as the Signals unable to take proper breaks between tours.

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