SINCE INTERNATIONAL seminars on nuclear warfare may be going out of style for a while, I will report on one that I attended in August, before the plane went down. It was in Erice, an out-of-this-world walled town at the top of a steep hill in northwest Sicily.

Elizabeth Shannon, whose husband William, our former ambassador to Ireland, was a participant, told me she thought that, after we left, Erice would be rolled up in the mists that enveloped it every morning and disappear like Brigadoon.

It was what you might call an irrelevant setting for the third annual discussion of nuclear dust and civil defense and laser beams, but in some ways it was not.

Its principal attraction, a Norman castle with crenelated walls and battlements, was an apt expression of security-consciousness in another age. It was a medieval AWACS in stone, commanding a breathtaking view for miles around of land and aquamarine sea. Its limitations are inscribed in Erice's invasion-studded history. The Germans overran it in 1184.

The monastery where many of us were housed offered another example of the limits of technology. The dryer in the basement of the Majorana Center for Scientific Culture, as eminent scientists with dirty socks discovered, gave back clothes that came out soggy after two hours of futile churning. Several Nobel wives importuned their mates to make the technology feasible, but nothing happened. By the fourth day, people were taking their damp clothes to the roof to dry in the dazzling Sicilian sun.

It so happened that defensive weapons systems and feasible technology were the subjects of discussion on Aug. 19. That was because Edward Teller was the great star of the conference. The Hungarian-born father of the H-bomb is also the godfather of President Reagan's much-mauled "Star Wars" concept of a nuclear shield. Teller, a tall, stooped, compelling figure is the Kissinger of science. He has the accent, the brilliance, the ego and the capacity to arouse rage and reverence in almost equal measure. At Erice, he was surrounded by worshippers and proteg,es -- the largest delegation was from Livermore, the laboratory he created in the 1950s, when he sensed H-bomb faintheartedness among Los Alamos colleagues, and began his feud with Robert Oppenheimer.

At Teller's side in the front row of the conference was another nuclear stalwart, Dixy Lee Ray, the sturdy, silver-haired, sneakered former governor of Washington and former chairman of the Atomic Energy Commission.. The first day, Teller addressed the group in tones of basso profundo reproach. The press had misinterpreted and distorted his suggestion for a nuclear defense shield, he said.

Soviet delegate Moisey Markov, a hulking, raw-boned, sunburned man who looked like an Iowa farmer, also talked on the first day. He said, laboriously, "Love Thy Neighbor." A Livermorist told me it was "inappropriate."

But what the Livermorists found much more "inappropriate," it developed, was the opposition to Teller. Richard Garwin, a veteran of the technological wars and no dove, first annoyed them by talking about a possible conventional defense of Europe. He irked them further and more seriously by suggesting that if a secret poll of defense system researchers were taken at Livermore, the deepest questions about its feasibility would be uncovered.

The resentment at Garwin boiled over at a birthday party on Aug. 22 for me and Bill Shannon. Conference chairman Antonino Zichichi, a life- loving Sicilian scholar, had arranged for three pastas and singing by delegate Markov's red-headed daughter. Her smoky Russian ballads brought us briefly together. Asked for a response, I sang "Down by the Riverside" -- with its chorus of "I ain't gonna study war no more,", which I hoped was in the spirit of the seminar.

On the way out, Dixy Lee Ray said we should have sung "The Stars and Stripes Forever." Back in their monastery, she told Garwin, in front of his wife and two friends, "I think you are a traitor."

Garwin, a pale, smiling man who is rational to a fault, replied equably, "That word has a specific, technical meaning. Shouldn't it be reserved for war time?"

Dixy Lee Ray did not retreat, then or the next day, as word of her charge swept through the seminar. "I think it applies," she said tersely. Garwin should not have aired differences about the defense of Europe, or "doubts that do not exist" about Teller's nuclear shield.

On the last day after a final burst of brilliance from Teller, the conference voted to appoint a committee -- consisting of Teller, Zichichi and Eugene Velikhov of the Soviet Union -- to study the feasibility of a nuclear defense.

"It's always the same with Edward," sighed a non-Livermorist. "When it's a question of more or less weapons, he always wants more."