WASHINGTON – Eighteen months ago, John Dullahan was an intelligence analyst with a long and varied career in both the military and the classified world. Today, he is jobless and blacklisted from the federal work force, his loyalty to the United States, he says, brought into question.

He just isn’t sure why.

On St. Patrick’s Day 2009, the government stripped the Irish-born Dullahan’s security clearance and fired him from his job at the Defense Intelligence Agency in a manner that has no precedent at the Pentagon — invoking a national security clause that says that it would harm the interests of the United States to inform him of the accusations against him.

As a result, Dullahan, a Vietnam veteran who served at military posts around the world and as a U.N. weapons inspector in Saddam Hussein’s Iraq, cannot appeal to a board of senior agency officials, as others in his position might. He is, in effect, stranded.

“This has been devastating for me,” said Dullahan, 65, who became a U.S. citizen in 1973. “I am a loyal American.”

Security clearances are a ticket to opportunity for hundreds of thousands of federal workers and contractors. But when those clearances are taken away, so is any chance of employment in the national security complex.

The reasons to revoke a security clearance can vary. Some federal workers lose them because they are found to be using illicit drugs. Others lose them when they are determined to be financially vulnerable, a situation that might make them susceptible to blackmail.

Dullahan was fired after apparently “showing deception” during three polygraphs — each time when he was asked whether he had ever spied for the Soviet Union. That, at least, is his best guess as to the reason for his termination.

“We just don’t know what it was that caused DIA to do what it did,” said Mark Zaid, Dullahan’s attorney. “Presumably it’s connected to the polygraph, but at what level we just don’t know. What happened to John is extremely rare. It doesn’t happen. I’ve had dozens, if not hundreds, of cases where people have failed their polygraph and been accused of drugs, espionage, you name it, and they have all gotten due process.”

Dullahan’s case is all the stranger because his wife continues to work at the DIA as a supervisor with access to what the government calls “Top Secret/Sensitive Compartmented Information.”

“I have access to the crown jewels,” JoAnn Dullahan said.

Dullahan is challenging the DIA’s decision in federal court on the grounds that he was denied due process.

Dullahan says the root of his current problems may lie in Damascus. In 1985, he began three six-month rotations through Syria, Lebanon and Egypt while assigned to the U.N. Truce Supervision Organization.

At the time, he socialized with some Soviet officers, and on one occasion with a Soviet diplomat, he said. A German friend who visited him in Damascus spoke Russian with some Soviets at one social function.

One of Dullahan’s fellow officers found it all suspicious and reported him to the defense attache at the U.S. Embassy. Called in, Dullahan was questioned about his contacts, as well as about his time stationed in Germany and a visit to East Germany, he said.

The defense attache said that Dullahan’s German friend was a spy and that he was being groomed for recruitment. Hanging in the air, Dullahan said, was the suggestion that he had already crossed over.

“I’d been in combat, but I had never experienced anything like this; I couldn’t sleep,” Dullahan said. “I really identify with being an Army officer. This was my very being.”

The matter was dismissed when Dullahan’s commanding officer flew in and backed him. But Dullahan’s wife believes that her husband was traumatized and permanently marked by the experience.

“That whole thing in Syria was such an assault on John’s honor,” she said. “That’s why it got him so viscerally. It was an attack on his person. It has festered for 20 years. And I think he was re-experiencing it all when he was sitting in the chair” for the polygraph. She believes he failed the tests because the memory of that time surfaced and took hold.

In 1986, Dullahan moved to the DIA, where he worked on the Afghanistan desk, then with the newly independent countries of Eastern Europe. In 1992, he retired after failing to make colonel, but got a civilian position at the DIA in 1997.

In early 2008, with the permission of Dullahan’s DIA superiors, two FBI agents visited him at his office at Bolling AFB in Washington and asked whether he would be willing to participate in a classified, black program. Dullahan readily accepted the offer.

But first he was asked to take a polygraph at an FBI facility in Baltimore. An hour or so into the examination, Dullahan was questioned about espionage and whether he had ever worked for another power.

The examiner said he was registering deception and left the room. After 90 minutes, the examiner returned and said, “Let’s run this again,” Dullahan recalled.

“He tells you the questions he is going to ask,” Dullahan said. “I am going to ask: Did you ever spy for the Irish government? Did you ever spy for the Syrians? Did you ever spy for some other country? The last one was the good one. Did you ever spy for the Soviet Union? You know it’s coming and you know it’s the one you have to pass. And your heart starts pounding.”

The examiner said he registered deception again.

Dullahan was offered and apparently failed a second polygraph on the same set of questions. The DIA also organized its own polygraph, and Dullahan failed a third time, also apparently on the same set of espionage questions.

In February 2009, Dullahan was called down to a security office at work and placed on administrative leave. The next month, he said, he was called back in and offered the opportunity to leave quietly with retirement benefits. If he refused and challenged his firing, he said that he was told the alternative was no retirement and termination on national security grounds.

Dullahan said he was told that he had to make a decision before leaving. After consulting with his wife, he refused.

“I said I wouldn’t accept if it was a million a month,” said Dullahan. “I saw it not just as a job but a calling, as an officer and at DIA. And regardless of the outcome I will remain a devoted, loyal American.”