LONDON, AUG. 30 -- Free at last after 52 months of captivity, former hostage Brian Keenan spoke today in a soft, breaking voice about his long nightmare and the friends he was forced to leave behind.

There were tears and swallowed words and long, anguished pauses as Keenan tried in slow, measured tones to describe to a press conference in Dublin the loneliness and the fear, but also the comradeship that developed among the Western hostages he knew in Lebanon.

There was also a plea to the press to exercise restraint. Keenan said American press reports suggesting that the last two hostages who were released had carried information their kidnappers did not want divulged had almost led to the execution of some of those still held.

"All of us are but teeth on a comb, and if one of us is snapped off in a sudden rage, it cannot, cannot be put back," he warned, adding of his captors, "You must remember that hysteria with these men is not subject to reason."

Keenan, a 39-year-old school teacher from Belfast, was released last Friday by his pro-Iranian kidnappers in Beirut. But the world paid little attention, riveted by the drama of thousands of other Western captives in Iraq and Kuwait.

Keenan began with words of self-definition. "Hostage is a crucifying loneliness, a silent screaming slide into the bowels of ultimate despair," he said.

"Hostage is a man hanging by his fingernails over the edge of chaos, feeling his fingers slowly straightening. Hostage is the humiliating stripping away of every sense and fiber of body and mind and spirit that make us what we are.

"Hostage is a mutant creation, full of fear, self-loathing, guilt and death-wishing. But he is a man . . ."

Dressed in a T-shirt, blue jeans and wearing tinted glasses, Keenan spoke in loving detail about each of the three men he served time with, including Terry Anderson, who was the chief Middle East correspondent for the Associated Press. Anderson was captured March 16, 1985, and is the longest held of the Western hostages.

"Terry's a bit of a bulky and a belligerent man . . . who had a voracious hunger for intellectual conversation and when he did not get it would pace the floor endlessly in his patched and repatched and much more patched, but still very holey socks," Keenan said.

Keenan said he and Anderson, 42, whom he last saw 11 months ago, would pass nights talking about Anderson's daughter, Gabrielle, born after Anderson was kidnapped. Anderson would also describe in great detail plans for a school for young delinquents that he hoped to build in the United States after his release.

Keenan said Thomas Sutherland, a Scottish-born American who was the acting dean of agriculture at the American University of Beirut, was in some ways the least prepared for his long captivity. Yet Sutherland, 59, who has been held since June 1985, fascinated the others with long lectures on genetics and animal husbandry, two of his academic specialities, and on his beloved 1963 Volvo. "They came to us in those awful places as a kind of light illuminating out darkness," Keenan said.

But Keenan reserved his most emotional plea for his "soul mate," John McCarthy, 33, the British television journalist with whom Keenan spent much of his four years in captivity. McCarthy's wicked sense of humor and love of life had seen both of them through desperate times, Keenan said.

Although he tried to resist being released without McCarthy, Keenan said his captors finally forced him to leave. Asked how McCarthy might feel now that he was gone, Keenan said, "It is like a man who calls and takes away your right arm and walks away. But John is a very strong man now and although he will be very depressed for some days . . . I know John and he will come through it."

Keenan generally avoided discussing political issues , but criticized the British government for inaction concerning McCarthy's release. "John McCarthy's a great giver," he said. "It is now time for some people to start giving for John McCarthy."

Keenan described conditions of filth, bad food and random violence he said he and the others were subjected to. "Tiny, tiny cells, constant blindfolds, prolonged days in the dark, sometimes weeks without light, create kinds of insanity that drive men deep, deep into themselves," he said.

His captors were "men of 30 years old perhaps, with a 12-year-old mentality. . . . They have access to power on a personal level that they are not developed enough emotionally or psychologically to contain. Sometimes they just could not control the urge to beat very badly."

But Keenan said he felt "no desire for retribution." That would be "self-maiming," he said.

Instead, he spoke of holding a baby a few days ago at the Dublin hospital where he is recuperating. At that moment, he said, "I felt more alive than I have ever felt."