Bulgaria, a Balkan country on the Black Sea, has an area of 44,000 square miles, about the size of Ohio, and a population of 9 million. It is bounded on the north by the Danube River and most of the country is mountainous, with a climate similar to that in the central United States. PEOPLE

The population density is one of the lowest in Eastern Europe. Ethnic Bulgarians, in which the government includes an estimated 250,000 Macedonians, account for about 88 percent of the population; ethnic Turks make up 9 percent and the rest are Russians, Romanians and gypsies. The Bulgarian language is Slavic and, like Russian, uses the Cyrillic alphabet. Bulgarian Orthodoxy is the chief religion but religious activities are officially discouraged. HISTORY

Slavic peoples living in the region absorbed Turkic tribes that moved north into it in the late 7th century, and through the Middle Ages there was a succession of Bulgarian kingdoms. Later, for 500 years, until the Russo-Turkish War in 1877-78, Ottoman Turks ruled Bulgaria. An independent Bulgarian kingdom was reestablished in 1908, with its territory including portions of ancient Thrace and Macedonia. Bulgaria sided with Germany in both world wars and in 1944, when negotiations began toward an armistice with the western Allies, a Communist-dominated coalition seized power and Soviet troops entered the country. The monarchy was rejected by a referendum and a People's Republic was formed in 1947 that, with revised constitutions, remains today. GOVERNMENT

The Communist Party governs Bulgaria through party bodies and a National Assembly, an elected legislative body that ratifies the decisions of the party. The Communist Party and the small, allied National Agrarian Union are the only authorized parties. Todor Zhivkov, 73, has headed the Communist Party since 1954 and later became president as well. FOREIGN RELATIONS

Bulgaria, a member of th Warsaw Pact and Comecon, the Eastern Bloc's common market, is the most undeviating ally of the Soviet Union, partly because of the history of Russian protection from Turkish invaders. It also has worked to normalize relations with Balkan neighbors Greece and Turkey although the issue of ethnic Turks in Bulgaria has caused problems with Ankara. Between 1968 and 1978, Bulgaria allowed 100,000 ethnic Turks to emigrate. Relations have also been strained with Yugoslavia over the issue of ethnic Macedonians in Bulgaria. ECONOMY

Until World War II, Bulgaria was a agrarian nation, but since then industry -- including metallurgy, machine building and textiles -- has been developed and now only about 23 percent of the work force is still in agriculture. Since 1979 Bulgaria has adopted Hungary's model of the New Economic Mechanism, which emphasizes decentralization and local self-sufficiency, but as recently as two years ago, 75 percent of its foreign trade was with other Comecon countries.