Equipped with reporting talent and a warmth and understanding towards the Americans and their culture, An spent much of the later part of the war as a staff correspondent for Time magazine - the only Vietnamese to reach such a position in the American press. As dozens of leading American reporters flocked to his side for crumbs of insight over coffee in Saigon's Cafe Givral, An was working for Hanoi, feeding covert reports to handlers hidden in under- ground tunnels in Cu Chi, outside Saigon.

But there's another side to the tale. As stories of An's real work and betrayals grew in the years after the war, remarkably so did understanding and tolerance of his actions in the minds of many former American and South Vietnamese colleagues and sources, including such celebrated reporter-authors as David Halberstam and Neil Sheehan.

In 2003, towards the end of his life, An was even invited by the US consul-general in Ho Chi Minh City aboard the USS Vandegrift, the first US warship to visit since the fall of Saigon.

An didn't live long enough to see his son, Hoang An, serving as a translator for Vietnamese President Nguyen Minh Triet while he hosted his US counterpart George W. Bush during a visit in November last year. After long post-war years treating their star agent with mistrust given his links to the US, Hanoi, too, has embraced his legacy.

US historian Larry Berman has done a readable job uncovering the shades and nuances of An's life in his recently released biography, Perfect Spy - the Incredible Double Life of Pham Xuan An. His story naturally carries a heavy American overlay, largely of redemption and reconciliation.

He has left plenty of room for more dispassionate accounts. Berman speaks of meeting An during repeated visits to Ho Chi Minh City in the last years of his life, talking for hours surrounded by pets in the shaded recesses of his villa or at the now state-owned Cafe Givral. An's worsening emphysema - the communist spy enjoyed his packs of Lucky Strikes - added urgency to the task.

'One of his most striking qualities was just how easy he was to talk to,' says Berman. 'An was a great conversationalist ... he could joke, he had this tremendous knowledge of history. He had a great, sharp wit and, unlike a lot of Vietnamese, he could relate to Americans very quickly.'

Berman acknowledges the internal tensions faced by a biographer attempting to probe the psyche of a man who lived with deception as a way of life. In the back of his mind, Berman says he always wondered whether An was simply 'spinning me'.

'I was very conscious of walking a line doing this kind of story ... I knew there were things he probably could never tell me,' says Berman. 'As a biographer, you can only get as much information as you can and tell the person's story as faithfully as possible and then it is up to the reader to decide.'

'It was a vastly different project to anything else I've done,' says Berman, the author of three other Vietnam works, including the respected history No Peace, No Honour: Nixon, Kissinger and Betrayal in Vietnam.

Unlike more detached works, an obvious warmth comes through in this book, as Berman, like so many before him, is struck by An's intelligence and humanity. 'Yes, in short, I liked him,' he says.

But there were times when the 'walls would come down'. Despite repeated questioning, Berman says An never came to terms with his role and the deaths that it lay behind. When pushed about the violent battles he helped plot and the thousands of deaths that resulted, he tells Berman that he never knowingly killed anyone.

An's tensions dominate the book. Remarkably, Berman insists, An played it straight as a reporter, not giving in to any temptation to mislead his colleagues in his extensive cafe briefings or write loaded stories for publication.

'He knew he had to be as good a reporter as possible because if he didn't, he was dead,' says Berman. 'It was that simple ... he realised that choice and dealt with that very early on.'

An may have been a good reporter, but he excelled at his real job, the 'lone wolf' agent, referring to his dark trade as a 'profession'.

He studied it, absorbing its risks and demands. An talks of two sacred taboos of spying: getting caught and not properly concealing information and sources. Amid the baggage of reconciliation, some of the most striking parts of the book are the operational details, known to fans of the espionage genre as 'tradecraft'.

Rather than risk regular meetings with his handlers at Cu Chi, An would hide film of his strategic assessments and reports in homemade spring rolls, slipping them to a woman street hawker, who acted as his courier. He wrote his reports in his study late in the evening, his villa guarded by his German shepherds.

Berman is also strong on details about the disturbing value of An's work. In the early 1960s, he obtained extensive documents and briefings from the South Vietnamese about how their US advisers were preparing to combat communist guerillas.

His reports for Hanoi allowed them to cope with US helicopter assaults and air power. Hanoi's military mastermind, General Vo Nguyen Giap, once declared that An's reports were like 'being in the US war room'.

Then came the Tet Offensive of 1968, when communist forces attacked major towns and cities across the South, even briefly occupying the US embassy in downtown Saigon.

It was a military defeat for the north, but a political watershed that split a horrified US.

For weeks in advance, An moved around Saigon, checking out potential targets, from wharves to fuel installations. He then covered the resulting violence for Time.

Two years later, his information helped northern forces intercept a major push by southern troops in Laos, operating without US assistance for the first time. About 10,000 southern soldiers died and the US lost more than 100 helicopters trying to rescue them.

Berman paints An as an intense nationalist who, despite his genuine liking of Americans and his many friends, saw the need to defend his country. He says An was never a 'hard-core' party man, and he eventually wanted to return to journalism in a Vietnam at peace.

'I saw in him a sadness at how things worked out,' he says. 'He was a very intelligent man.'

Perfect Spy by Larry Berman (Collins, HK$208)