San Diego — To his parishioners in Old Town and Rancho Bernardo he was just another aging priest come West to enjoy a good-weather parish. A reward for years ministering in frigid Minnesota.

To the fellow priests he assisted for four years, like Father Alphonsus Moloney of Old Town's Church of the Immaculate Conception and Monsignor Lloyd Bourgeois of Rancho Bernardo's San Rafael church, he never spoke of "that episode," so they never asked about it.

"I believe he was involved," says Father Moloney. "He got some calls here. Some interviews, television and radio people. That way I heard about it. But it never came up, so I respected his confidence."

The priest in question is Father Walter Halloran. "That episode" was an exorcism that took place half a century ago in St. Louis, Missouri, which formed the basis for William Peter Blatty's best-selling 1971 novel The Exorcist. The movie starring Linda Blair soon followed in 1973. In the weeks leading up to this year's 25th anniversary re-release of the movie, Father Halloran has been besieged by reporters seeking interviews for magazines and television.

The publicity is a big change for the 76-year-old Jesuit. For most of the 50 years since it happened, he has kept his silence. Back in 1948 Walter Halloran was a 26-year-old trainee priest when he got caught up in what has become the country's most notorious exorcism.

"I'd been driving Father Bowdern around a good bit. [William Bowdern, then 52, had been charged to carry out the exorcism.] He had some difficulty seeing, so he used to ask me to drive him when he had calls to make. This seemed to me to be a request like many others."

It wasn't. Although Linda Blair plays the possessed girl in the movie, in real life it was an 11-year-old boy, Douglas Deen, whose fits and violent behavior began after a favorite aunt died. She had taught him how to use the Ouija board; it was when he tried to contact her spirit that the trouble started.

His blue-collar parents took him to a barrage of doctors and psychiatrists who all declared Douglas did not have definable mental or physical problems. So Deen's parents, despite the fact they were Lutherans, asked Catholic authorities for an exorcism.

"I didn't [even] realize it was an exorcism until I got there, and Father Bowdern started using the ritual," says Father Halloran, speaking from Minnesota, where he has returned to be with his family. "I recognized the prayers by the wording. I said to myself, 'This is an exorcism!' "

It is the first night he remembers most vividly.

"That first [evening] Douglas had gone upstairs and changed into his pajamas. He was lying on the bed, covered with a sheet. Father Bowdern started out by saying a couple of decades of the rosary [a decade is ten Hail Marys] and went into prayers of exorcism. There's a prayer to [the Archangel] Saint Michael asking for his help and asking our Lord to drive this person out. For instance, 'Evil Spirit, leave this person!' And a number of questions: 'What is your name?' 'What is the day and time that you will separate yourself from this person?' "

"Douglas was just lying there. The reactions came generally when there would be an invocation of Saint Michael or the Blessed Mother or our Lord. He'd start thrashing about. Those things seemed to trigger a physical reaction from him.

"Most of the time during the exorcism I was holding the child, restraining him from injuring himself or those around him. He was strong as any young boy would be. You got kind of fatigued restraining him after about four or five hours."

The young seminarian Halloran was struck by the repetitiousness of Father Bowdern's attack. "The only thing that you do is recite the prayer for exorcism that's in the ritual. You don't do anything else. One of the cautela [warnings] that are given you [is] that you don't enter into conversation or make deals with the evil spirit. Like saying, 'I'll fast for 40 days if you depart from this person.' You can't do that. The devil or the evil spirit is much more capable than we are, and to negotiate with him would be admission of at least his superiority, or control, in this case."

Halloran says his biggest problem that night was believing what was happening before his eyes. Especially when the bed started rising.

"I have never seen this before or since. The bed started going up and down. You see it, and the first question is, 'Am I really seeing this or not?' And I guess I had a surprised look on my face, because that's when Bowdern said, 'Just relax, and keep on praying.'

"So I was kneeling there and saying the prayers, and the bed was rising and settling and rising and settling. I don't remember whether it came off the floor or not, but the bed, and the springs and the mattress would rise up and then go down, rise up, and then go down. Six inches to a foot. I was kneeling there, and my elbows were resting on the bed. It wasn't being caused by the kid."

Halloran was to feel the possessed boy's wrath too. "When he'd start to thrash around, I'd hold his arms and hands so that he wouldn't hurt himself. Once he swung his arm and he got me on the nose. Broke it."

Halloran held on, battered, feeling he was actually seeing evil manifested for the first time in his life. "I saw a holy water bottle sitting on a dresser, and all of a sudden it came flying across the room. It missed me by about a foot. There wasn't anyone near it, so no one could have thrown it. It hit the wall and fell on the floor behind me."

Some of the events, Halloran believes, have less than supernatural explanations. "Sometimes the boy would say things in Latin. He didn't have a proficiency in any other language than in English, but he could very easily have done that just in mimicry because the prayers were being said in Latin. It was mostly a repetition of what father Bowdern was saying. Then sometimes his voice would be low, other times a falsetto. But that could be done by any kid.

"The child used to hum, in some cases sing, a little snatch from an aria, but it wasn't indicative of his having received powers of an operatic singer. Again it was mimicry. He picked it up someplace."

For other events, Halloran has no rational explanation.

"What is your name?" demanded Father Bowdern ("Father Merrin" in the movie, played by Max Von Sydow), according to the exorcism ritual. "Dicas nomen tuum!"

"And the child answered, 'I will answer to the name of Spite!' "

Halloran is not sure if the child went on to say, "I am the devil himself!"

"But I was there when the word 'Spite' appeared on his body. And that was very visible. Unmistakable. On his back right shoulder."

The first session ended at dawn, with boy and priests exhausted. "On the way back -- it was about five o'clock -- I asked Father Bowdern, 'Am I supposed to be doing this again some time?' And he says 'Oh yes. You're part of the group now!' "

The thing that shocked Halloran most was what he saw as witnessing the reality of evil. "It buttressed [for me] that evil does exist, and that in many ways we're powerless to do much about it. You have this nice, easy life, then suddenly, this. You're impressed by your frailty. But then the other thing that impressed itself on me was the efficacy of prayer, of using the prayers set aside by the Church to effect removal of the evil spirit."

Yet night after night, for three weeks, the priests would turn up for battle and retire at dawn, defeated and exhausted. One regular phenomenon was the markings. "The child would say, 'My leg is hurting.' You'd look at his leg, and there would be marks, kind of like claw marks, on his legs. And the same thing on his back and his chest. Sometimes words would appear that would be very evident. We were careful not to try to read into anything. Something specific like 'hell' would appear and very visibly, sometimes arrows would be scratched into his skin and numbers would appear. If they did have any meaning, I don't know what it was. Like the Roman numeral 'X' [ten] or 'V' [five]. No names.

"On Holy Thursday, the day of the feast when Christ instituted the blessed sacrament of the Eucharist, I asked the child if he knew anything about it. He says, 'No.' I said, 'Would you like to?' He says, 'Yes.' So I told him about the Last Supper, and he started squirming. He says, 'It's starting to hurt again.' He complained much more about the pain than he had before. He opened up his pajama top and his whole chest was covered with markings. He obviously didn't do it to himself, because his hands were in complete view. I said, 'Would you like to have me stop?' He said, 'Please.' So I did. Then later on that night I said, 'Do you want to try it again?' He said, 'Okay...' And I said, 'Look, if you start having pain or anything, just tell me.' And the marks started to appear again. He said, 'Let's stop.' "

Halloran was taken off the case after about three weeks, because he had philosophy exams to face. By this time the boy had been moved to the Alexian Brothers Hospital.

Father Bowdern kept him informed. "He said he would ask, according to the ritual, 'What is the day and time that you will separate yourself from this person?' And the child would say, 'I will not leave until the secret word is pronounced. This boy will never say it.'

"And that's a reference to a passage in the Old Testament where there's a confrontation with the devil," says Halloran.

But finally, after ten more days, just before Easter, everything changed.

"The child finally said the secret word, 'Dominus,' " says Halloran. "It was an admission on the part of the spirit that God was superior to him. 'Dominus' means 'Lord' in Latin and is the word used to identify Christ. It carries a statement of power and superiority."

Douglas Deen (now 61 and a priest himself) told Bowdern on that last day he believed it was Saint Michael the Archangel who entered his body and uttered the word.

"Father Bowdern told me of the final moment," says Halloran. "They were saying the prayers of exorcism. Douglas seemed to be in a deep, deep sleep. And he woke up and he said, 'It's over. He's gone.' And at the same time there were a number of priests over at the college church saying a breviary, saying their prayers, and a huge, bright light lit up the sanctuary of the church, and then there was a loud report [bang]. It was interesting because most of the people in the [Jesuit] community didn't have any idea that this exorcism was going on at all until Bowdern told some of them the next day."

Halloran says Father Bowdern was so exhausted by the experience he never did recover. Douglas Deen remembers nothing of the entire period he was possessed. But he has named his own son Michael, after the Archangel.

So now, 50 years later, does Father Halloran still believe the boy was possessed? "I never went to the trouble of trying to determine in my own mind whether it was a case of possession or obsession," he says. "I witnessed certain things. I was just finishing up getting a degree, and in a month or two I was out teaching. Having several classes of 40 high school boys doesn't give you a whole lot of time for research. I don't know why I wasn't impelled to go after [the subject]. I guess I'm just not the scholarly type. My reaction was that the child had been submitted to all kinds of examinations and tests by medical people. I accepted their judgment, that it wasn't a case of being medically or psychologically unsound. And there couldn't have been any [ulterior] motive on the part of an 11-year-old kid. And the family -- all they did was suffer bewilderment, for a month and a half before they called us in."

And what about The Exorcist, the movie, with its scenes of Regan shooting out green bile and turning her head 360 degrees?

"That's utter nonsense. Nothing like the bile or the spinning of the head ever occurred. Or the urinating on the crucifix, or the scene where the little girl was whipped around the bed like a whiplash. Crazy! Just an attempt to appeal to the prurient excitability of people. I was so angry the first time I saw it.... I'm not great for self-flagellation. I won't be watching the movie next time it's released."