ONCE YOU MET HIM, Arthur Koestler was the kind of man you never forgot. I knew him long ago, in another country, and only for a short time, and yet I felt a deep loss when he died recently in London.

That he died a suicide mattered not at all to me. No one who knew Arthur Koestler could accuse him of cowardice. Intellectually fastidious, and in the grip of a debilitating disease, he refused to die a messy death.

In life, as in death, he did it his way. And he was so right so many times so far ahead of his time that if sometimes he was wrong, it was easy to forgive him.

In an era of creeping mediocrity, he was one of the towering literary and intellectual figures. More than any other man, and long before I met him in Japan years later, Koestler helped shape my political thinking and that of thousands of other Americans and Europeans who came of age in the the '30s.

He was the thinking man's anti- communist. He had been there. He had seen the future and it did not work. And he wrote about this disillusionment so brilliantly in "Darkness at Noon" and "The God That Failed" that he saved some of the rest of us the agony of the trip.

At the peak of his fame as a political clairvoyant, he renounced politics for other fields. "Cassandra has gone hoarse and is due for a vocational change," he wrote.

If he was celebral, he was also very physical. Arthur liked food, drink and women, especially women. Politics was the last thing on his mind when he arrived in Tokyo in the late '50s. What was very much on his mind was sex.

Besieged by his relentlessly hospitable Japanese hosts, Koestler retreated to my place in the country south of Tokyo to get some writing done. There, in a book of essays called "The Lotus and the Robot," he described his first reaction to the sensuous pleasures of Japan:

". . . an atmosphere with an erotic flicker like the crisp sparks from a comb drawn through a woman's hair -- a guilt-free eroticism which Europe has not known since antiquity.

"I responded to all this all the more readily as, coming from India, I felt as if I were suddenly emerging in my bathyscaph from the pressure of the black deep, with its tangles of ghostly seaweed and primeval monsters, into a brilliant, sunlit world.

Thrilled he was and respond he did, especially to the Bar Lido, a tiny basement oasis near the railroad tracks in back of the old Imperial Hotel. The Lido was owned and operated by three sisters named Yoshiko, Fumiko and Michiko.

Their operation was solidly based on reverse racism: They catered only to foreigners, which in those days meant mostly American men, many of whom sought solace at the Lido when misunderstood by their wives.

Some pretty and talented girls worked at the Lido. One had a superb collection of Charles Addams cartoons, another could quote Oscar Wilde's fairy tales without end. Thanks to a generous sponsor, one of them went away to college in America and wrote back saying the campus was lovely but the boys didn't know what to do.

It was clear from the start, however, that Arthur had eyes only for Michiko, the youngest and prettiest of the three sisters. Arthur had a way of letting you know when he no longer needed you.

He disappeared. Michiko disappeared, too. When they surfaced days, perhaps weeks later, both seemed refreshed, cheerful and somehow younger.

Arthur loved women and loved falling in love with them. But he told me later that he really fell in love with Michiko when she offered to lend him money. He was so touched he was speechless.

Arthur had told her that he was a writer, but he did not tell her that he was rich and famous. Michiko thought all writers were, by definition, poor and struggling.

"Did you take the money?" I needled him.

"Of course not," Arthur said indignantly. "What kind of man do you think I am?"

"Frugal," I said. He was, too. Arthur was always a man of the left, but he had a great respect for money.

Early one morning several years later my phone rang and a thickly accented voice said: "Vere is the Lido? Vere is Michiko?"

I explained to Arthur that the Lido was no more, that Yoshiko had gone her own way and Fumiko and Michiko now had their own bar in Akasaka. It was named The Eve.

At lunch, Arthur told me that he was back in Tokyo because Life had offered him a large sum for an article on Japan. But the real reason he was back, he said, was to see Michiko. Besides, he added, he was 59 and afraid that he was becoming impotent.

On the way to The Eve that night Arthur Koestler, man of the world, fretted like a schoolboy. "She won't remember me," he said nervously. "It's been too long."

In The Eve the waitress brought us beer. Michiko glanced up from another table, where she was chatting with some customers, and nodded politely. Later she came to our table to assure Arthur that she was happy to see an old friend.

Arthur was inconsolable. "Let's get out of here," he muttered, and we left. But after midnight, when I knew the crowd would be thinning, I took us back to The Eve. Sure enough, this time things were different.

When we met for dinner three days later, Arthur never seemed more relaxed and self-confident. Obviously all his doubts about his manhood had been resolved in his favor.

That is the way I like to remember this small Hungarian with the large head who, in "Darkness at Noon," a novel based on the Moscow purge trials, told me how a man could confess to crimes he had never committed, and who, in "The God That Failed," forever demolished the myth of the Communist utopia.