THE SCHOLARS and policy-makers of the time called it "the great game": the 138-year struggle between the British and Russian empires to dominate a harsh central Asian land of fiercely independent shepherds and farmers.

In 19th-century Afghanistan, it was the British who seemed to have the upper hand. From the frontier of British India, they periodically invaded the Hindu Kush to ensure that successive Afghan kings performed dutifully their role as buffers, keeping the Russians at a safe distance from the crown's most precious colony.

"Fighting him was good shikar," a Pushtun tribal elder says of the British invader. He speaks in the opening pages of Edward Girardet's book, perhaps glossing the past with nostalgia: "We respected each other. We could look one another in the eye. We had certain rules."

But, in the Afghan guerrilla war against a 20th-century invader, the Soviet Union, Girardet writes that there are no rules. "The 'Great Game,' if it ever truly displayed a sense of fair play, has become a gruesome, pitiless contest of strength, endurance and basic survival, for the greater part ignored and forgotten by the rest of the world."

Of all the wars and crises along the front lines of the current superpower "great game," the mujaheddin's resistance to the Soviets is the least accessible, least reported and least understood. For those wondering just what is going on there (and who suspect that it's more complicated than the CIA agent's romp through the Panjshair Valley in Ken Follett's 1985 thriller, Lie Down With Lions, there have been few readable books to learn from. Girardet's is the most comprehensive, and perhaps the best, English-language book so far to explain the Afghan war to general readers.

Girardet first reported from Afghanistan three months before the Soviet invasion in 1979, and has been back six times since then for the Christian Science Monitor. Among his firsthand observations of this bloody stalemate are vivid accounts of its brutality. From a 1981 trek through Nuristan, a mountainous eastern province, Girardet writes:

"Long thin waterfalls plunged down narrow gorges, their rising vapors nurturing mini-oases of ferns, mosses and trees, while dozens of streamlets laced their way across verdant slopes. . .

"Mines had not occurred to anyone. The caravan was hardly two hours inside Afghanistan when some of the mujaheddin up front stopped to make tea. Waiting for the rest to catch up, a young Panjshiri, Shah Mansour, crossed a small stream to hunt for firewood among the bracken and wild rhubarb on the other side. Suddenly, a sharp explosion and his right foot was severed below the ankle, a bloody mess of flesh and bone. A few feet away lay the pathetic remains of his black plastic shoe and the metallic fragments of a booby-trapped watch." THE BOOK'S central feature, though, is Girardet's balanced reporting and analysis of the bewildering complexities of this war and the tradition-bound Islamic society in its grip. Largely because of these questions, Girardet's book is not an invitation to a casual reader to stay up all night. You have to be interested in the topic.

Americans should get interested. With the Reagan administration reportedly including high-tech Stinger anti-aircraft missiles in U.S. arms shipments to the guerrillas, Girardet tells how the mujaheddin, mostly unschooled, misuse even much simpler weapons.

Girardet describes how barriers of tribe and tradition among Afghans, built on centuries of conflict and mutual distrust among the many ethnic groups, have helped keep the resistance fractured. He also identifies the trends and personalities, such as young commanders inside the country, that tend to work toward the unity that will be essential to strengthening -- even perhaps maintaining -- the resistance.

These complexities and rigidities of traditional Afghanistan must be understood by anyone, including the U.S. government and the increasingly active private organizations in America, who think to aid the Afghans.

Girardet is a reporter who seems to relish whacking through the bush of obscure lands and writing home about it. Last year he sat on a pile of Afghan rugs in his Paris apartment, grimacing at a small computer screen as he edited his book. "I've had enough of Afghanistan for now," he said, and launched into a description of a planned trek along the length of Africa.

Girardet's own multi-cultural background, which included schooling in five countries, gives him some of the essential flexibility to report from strange and distant datelines. It also affects his speech, which is vaguely British-accented and can drift almost unconsciously from English to French and back again. It may be this same background that produces an odd turn of language in the book, which is sprinkled with mixed metaphors and juggled jargon. Intending to explain how the dominant Afghan ethnic group represses a minority of Mongolian origin, Girardet writes "Pushtuns . . . have traditionally treated the Hazaras as underdogs."

Also, the book's dedication, "to those for whom freedom is worth fighting" seems not exactly what was intended.

Girardet's Afghanistan has not been well-served by its editors, who let numerous spelling and typographical errors into print, and who might have added a glossary.

The book also suffers from some of the usual problems in dealing with Afghanistan -- such as the dearth of good maps. In my own trip into Afghanistan last year, for The Washington Post, the mujaheddin repeatedly asked me if I had any good maps of their country.

Another inevitable problem: statistics on Afghanistan and the war are rare and quickly go out of date.

Now that the Soviets are imposing themselves in Afghanistan as the British Empire once feared -- and as James Michener warned they might in his novel, Caravans -- a book such as Girardet's is essential. Recent American books on Afghanistan have been mostly scholarly -- leaving Europeans, particularly the French, to publish general accounts of the war for what seems a more interested public there than in North America.

Happily, Girardet's balanced and informed assessment of this war seems only a beginning for English-language readers. Collins publishers in England is planning a year-end release of a book by one of the most respected American researchers on current-day Afghanistan, Michael Barry. The book was first published as Royaume d'Insolence in France last year.