COUNTRY-- Afghanistan, a landlocked country in central Asia, has a population estimated at 21 million and an area of 260,000 square miles, about the size of Texas. The terrain is largely mountainous, with peaks up to 25,000 feet, and arid desert, with scattered, fertile irrigated valleys.

PEOPLE-- The population is a mixture of central Asian ethnic groups, dominated by Pushtun or Pathan, who account for 55 percent, and Tajiks, who make up 30 percent. Uzbeks, Hazara and Turkomans are also represented. The chief languages are Pashto, spoken by the Pushtun, and Dari, a derivative of Persian, spoken by the Tajiks. The unifying force in the country is religion: 99 percent of Afghanistan is Moslem, 80 percent of that Sunni and the rest, about a million, Shiite.

ECONOMY-- Afghanistan, primarily an agricultural country, has a per capita income of about $100 a year, one of the world's lowest. About 80 percent of the population engages in agriculture but only half the country's arable land is cultivated, mostly in wheat, cotton and fruit. Industry and natural resources have been little developed. Afghanistan produces natural gas, sending most of it to the Soviet Union. The Soviets account for 45 percent of Afghanistan's foreign trade, with the United States, Britain and Japan playing smaller but significant roles.

HISTORY-- Straddling major ancient trade routes between east and west, Afghanistan has been an arena for a succession of invasions and conquests. Some of history's most notorious invaders have seized the country, including Alexander the Great in 328 B.C., Genghis Khan in the early 13th century and Tamerlane a century later. Arabs who invaded in 652 A.D. brought Islam, which took strong root. In 1747 Ahmad Shah Durrani established an independent kingdom and in the 19th century, the British, from India, and the Russians from the north brought the first European influences. From 1880 to 1919, Britain conducted Afghanistan's foreign affairs, but the country was never a true British colony. After an Anglo-Afghan war in 1919, Britain withdrew and an independent monarchy was formed that, despite frequent internal hostilities, lasted until 1973 when former prime minister Mohammed Daoud, in a bloodless coup, took power and declared a republic. Daoud was overthrown by a leftist military coup in 1978. Nur Mohammed Taraki, who became president was slain last September and replaced by Hafizullah Amin, who was killed at the time of the recent Soviet invasion.

RELATIONS-- Since independence, Afghanistan has proclaimed a non-aligned, neutralist foreign policy, with its closest ties to the neighboring Soviet Union and cordial relations, from World War II until recently, with the United States. President Eisenhower visited Kabul in 1959, and Afghan leaders and U.S. secretaries of state exchanged visits regularly. The U.S. Peace Corps had some of its most succesful programs in Afghanistan. The Soviet Union, however, has been the largest donor of military and economic aid and has had a controlling influence in the country since the 1978 coup, which led that December to the signing of a 20-year friendship treaty.