The haunted world of the jihadi-hunter leaves little time for a normal life for this blunt and obsessive American.

Steven Emerson is on a mission to save the world. Let us agree that the world, daily convulsed with another bombing or fresh beheading courtesy of men invoking God, could do with some saving. What is not generally agreed on is where, precisely, responsibility for the mess resides. Over a decade ago, Emerson identified the enemy as jihadists – fundamentalist Muslims – and set out to understand them. He has concluded that no compromise is possible and that the western world risks submerging its own identity as it bends to intimidation from radical Islam.

Today Emerson's occupation – indeed, passionate preoccupation – is born of a world staring such irreconcilable differences in the face. As executive director of The Investigative Project on Terrorism, a Washington-based, non-profit organisation, Emerson collects data and intelligence on the activities of Islamist terrorist groups. What he and his two dozen or so staff unearth is provided to the US Congress, to the various arms of American law enforcement and to international media.

As we look out over Sydney Harbour, during Emerson's visit down-under to give politicians and intelligence agencies the benefit of his sleuthing, it is not the clatter of cutlery that accompanies our conversation as much as the sound of civilisations clashing. "I believe it's the number-one threat we face. It's the collision course between Islam and the western world." Emerson's deep conviction took root in his former life as an investigative reporter. While working for the US network, CNN in the early '90s, Emerson happened upon the story that would consume him. The degree to which radical Muslims had infiltrated the United States and exploited its liberties in order to undermine it, was for Emerson more than just a story. "This was an important issue that went beyond the typical conviction that a journalist might have, that drives him to put a story on the air. The story gets on the air and then moves on to something else. I wasn't willing to move on to something else. This tugged at the heart of our very existence ..."

Leaving behind his covetable six-figure salary at CNN in 1993, Emerson set up The Investigative Project and produced Jihad in America, a documentary where Emerson, under cover, exposed the blood-curdling language of incitement used by terrorists from Missouri to Florida. For his efforts, Emerson won a number of awards, including the prestigious George Polk Award for best television documentary. But alongside the prizes, he also acquired a lifetime's enemies. Despite insisting that encouraging and supporting moderate Muslims is "half of my mission", Emerson has been condemned by his opponents as an "Islamophobe", been the subject of two biographies (needless to say, unauthorised) by Hamas and received death threats.

In spite of this, Emerson has opted for a dangerous life. "If I paid attention to what was said about me in jihadist circles or their apologists' circles, I would be paralysed. And I'm not going to allow that to occur ... that's what they want to do, to paralyse me, to intimidate me."

When I ask about how this plays out in his everyday life, he takes cover behind, "There are issues that I have to deal with. It's a personal issue." There have been some obvious concessions, however. "I'm not doing undercover work any longer... I hung up my undercover days after the documentary. I was outed at that point. The actuarials," he says wryly, "would have changed dramatically, had I continued. But we employ others to do it ... freelance anti-jihadists, if you will."

Piecing together an accurate picture of the life led by jihad-buster Emerson presents a challenge. By his own reckoning, he is on the road around 200 days a year. Left to soldier on at home is his team of investigators; left to comb through tens of thousands of pages of evidence presented in court cases which may provide useful information; left to expose the ruses employed by terrorist organisations masquerading as charities; left to add to the 4 million documents and 18,000 hours of undercover audio and video collected by them to expose the enemy's objectives. The boss meanwhile, who insists on a paper trail and rejects intuition as a substitute, stays in touch through late-night email vigils in countless anonymous hotel rooms.

So what happens when you go home? "There is no home. There's a domicile."

Admitting that his domiciliary bed is permanently strewn with documents, Emerson remarks with a half-smile, "I go to bed with jihad and I wake up with jihad." And just to make his priorities plain, "when push comes to shove, if it's a choice between meeting with an FBI agent or meeting with a member of my family, guess who wins? ... I don't want to sound as though I am thoroughly antisocial, but the mission comes first. The party comes second. I'm not a party guy." This is telling me something I know.

Emerson presents as an enigmatic mix of wolf and lamb. During a lecture preceding our meal, I watch him reciting the dire news about jihad to a largely receptive audience. His delivery is solid. He could be a banker, were it not for his life-or-death message. The Emerson who is often described as abrupt and abrasive is nowhere to be seen. Then a long question from the floor, challenging him, reaps an unanticipated rise. Emerson turns intense, parrying with irony and ending with an agile thrust into his opponent's argument. "If I didn't want to be too blunt, I'd get pinstripes and work in the State Department. That's why I formed my own organisation, so I could be blunt," he tells me bluntly at dinner.

Which is probably why he feels like a finned creature on a sandbank when performing his duty as chief fundraiser for The Investigative Project. "I hate schmoozing ... I mean I'd be very content just reading my emails and responding in a hotel room, and not going out at all."

In truth, Emerson has dramatically limited his fundraising prospects. As a matter of principle, he does not accept money from religious groups, nor from the US government, shunning what he calls the "gravy train of homeland security". By the sounds of it, he has denied himself a river of gold. "The amount of money that has been given by the government since 9/11 ... you're talking about hundreds of billions of dollars – I haven't taken a penny. Sometimes I wonder maybe I should. But I won't. Because I don't want to worry when I'm testifying that I'm going to withhold criticism of a government agency or the FBI because I'm taking money from them."

Despite broadly supporting the work done by US law enforcement agencies, Emerson alludes to an underlying malaise. "If I were to publicly disclose the degree to which there is a dysfunctional common denominator to agencies, people would not believe it." Nor does he hold fire when it comes to Karen Hughes, whom George W. Bush hand-picked to repair bridges to the Muslim world. "When Karen Hughes runs into the arms of the Muslim Brotherhood in Cairo and says, ‘Oh forgive us, we're on the same page. We can agree on our values', we can't agree on the same values with the Muslim Brotherhood! There's no possibility of agreeing on their same values if they believe in the notion of sharia. I think that what she has done has been exceptionally detrimental to our national interest of upholding the rights of women, of pluralism, of democracy in the Muslim world."

Emerson's reputation in Washington was forged on the basis of testimony before the US Senate's Judiciary Committee in 1998, where he systematically laid out the jihadist threat to the US. He foreshadowed a terrorist strike on US soil. Three years later, when planes like poison arrows, pierced the Twin Towers of Emerson's hometown, he was accorded the status of prophet by many. But in the years preceding that strike, Emerson had been seriously questioning his own worth. "I almost came to the conclusion that I was totally irrelevant."

Irrelevant, but not wrong? "Not wrong. No, I never for one second [thought] I was wrong. The question was whether I was having any effect on people and I came to the conclusion prior to 9/11 that I wasn't."

So is he in the obscene position of having been proved right by the deaths of nearly 3000? "It was an affirmation of what I stood for, but on the other hand, was it worth it? No. Was it worth having 3000 people killed? Absolutely not ... would I [rather] be wrong? Yes. As much as it would pain me."

Emerson sets out the equation that determines whether his services are in demand, or not. People's focus on terrorism lapses, he says, in periods when there are no attacks. As soon as a terrorist strike occurs, public vigilance is restored "and the less important the role that I have to play because people respond to the market". I suspect only Emerson the Blunt could frame public security and mass murder as a calculation of supply and demand.

"It's a market response," he says, indicating the water dancing just beyond our restaurant window. "If there are bodies falling into the wharf here, I don't have to be in Australia trying to wake up people to the threat of terrorism. They'll see the corpses lying in the water. That's what happened on 9/11. I just stood back. Instead of having to make the phone calls before 9/11, [afterwards] I received the phone calls."

Emerson believes an attack on Australian soil is "very viable". He says: "You've got two areas of vulnerability. You've got one, due to being in the target range of Jemaah Islamiyah. And two, you have a critical mass of jihadists on Australian soil ... [who have] sufficient conditions to create jihadist cells that are not connected to external hierarchies like al Qaeda." He likens Australia's circumstances to that of the US. Both countries are operating "in this enigmatic environment of not knowing who's really a moderate".

Emerson reserves some of his ire for the editors here and elsewhere who failed to publish the Danish cartoon capers of the prophet Mohammed. "Are they worried about their own skin or are they worried about the national interest? Are they worried about Australians being attacked overseas? And if so, how does that always dictate what they publish anyway? If they discovered that Australians were abusing Iraqi prisoners, would they withhold reporting about that? Absolutely not."

And here Emerson bumps up against one of his principal anxieties: that the compromises the West has made with radical Islam are leading to a dilution of its own freedoms. He damns it as "cultural jihad" – the deliberate insinuation into Western society of fundamentalist Muslim elements masquerading as pluralist. While the West responds by tempering its own behaviour, the jihadis "by virtue of their vehemence and irrationality, [have] become much more leveraged in ... their ability to influence our behaviour – and I reject that!"

During the course of dinner, I notice Emerson's energy waning. Like a battery-operated toy, his gestures have slowed and his words have begun to trip over themselves. I remember something he told me earlier, "I rarely have the ability to step back from what I'm doing and look at the larger picture of life. Everyone tells me, ‘Steve, you need balance'."

His gives me his business card with its Washington address. "It's under false cover," he says, "so the card you have is a mail drop." I share a cab and deposit him at his hotel. A long night of emails lies ahead. "Look after me and I'll look after you," he says, before slamming the car door shut.