Long among the most economically successful and politically favored of the Soviet Union's East European allies, Bugaria shows signs of faltering under the aggressive new Kremlin leadership of Mikhail Gorbachev.

Boosted with Soviet support to one of the highest economic growth rates in Europe during the past decade, Bulgaria has plunged toward crisis this year as toughening Soviet terms have combined with bad weather, poor management and a crumbling industrial infrastructure.

A population of 9 million, accustomed to steady increases in its modest standard of living, now endures austerity measures ranging from daily cutbacks of electricity and curtailed shop hours to large price increases for gasoline, food and drinking water.

Life among the nation's political elite appears little more secure. The state planning minister was removed from his post and the economic bureaucracy drew sharp media criticism last month. Meanwhile, there have been growing signs of Soviet displeasure with Bulgaria's top leadership since Gorbachev's rise to power seven months ago.

During a visit to Sofia last month, Gorbachev pointedly noted that his discussions with aging Bulgarian leader Todor Zhivkov had included "ways to cope with the existing difficulties" and were carried out "without shunning the sharp edges." Three months earlier, the Soviet ambassador to Bulgaria more bluntly criticized the country's sagging labor productivity, the quality of its exports to the Soviet Union, and the failure to "proletarianize" the working class.

While still fortunate compared to its stricken neighbor Romania, Bulgaria appears to be entering a difficult period of both economic and political adjustment, diplomats here say. Restructuring of its resource-starved industries, forced in part by the restriction of Soviet largesse, could be matched by challenges for a Communist leadership long comfortable in its identification with former Soviet leader Leonid Brezhnev.

"There's no doubt that the squeeze is on," one western diplomat said. "The Soviets are out to rationalize the relationship. Zhivkov was close to Brezhnev. Now, it's a different generation."

Stepped-up economic pressure from Moscow is testing governments throughout Eastern Europe and predates Gorbachev's rise to power. Bulgaria, however, has been particularly vulnerable to increasing prices and demands for higher quality export goods. It conducts more than half of its trade with the Soviet Union -- more than any other East European country -- and is also more dependent on Moscow than any of its Communist neighbors for energy supplies and raw materials.

In the past, Bulgaria's ability to avoid the energy and foreign payments troubles of other Eastern Bloc countries was ensured by privileged deals with the Soviets, such as its purchase of oil at low ruble prices for processing and resale for dollars in the West.

The present cutback in Soviet assistance, however, appears as dramatic as the past generosity. Although official figures are secret, western experts believe Soviet supplies of oil to Bulgaria began to drop last year and this year may be as much as 30 percent lower than in the past. Significantly, the share of reexported Soviet oil in Bulgarian energy exports dropped by 50 percent between 1983 and 1984, and Bulgarian earnings from energy sales in the West decreased almost as much.

Stefan Stoilov, chief of the Economics Research Institute of the Bulgarian Academy of Science, said Bulgaria and the Soviet Union this month concluded a new agreement limiting Soviet energy exports to Bulgaria to the 1980 level for the next five years. "We have to change our attitudes from the time when energy cost next to nothing," he said.

The Bulgarians also have to accommodate themselves to Soviet insistence on higher quality goods to pay for the fuel and other imports. Signs of Moscow's dissatisfaction with Bulgarian manufactured products recently have been growing. Not long after the Soviet ambassador's public criticism, in an interview with a Bulgarian magazine in July, the Soviets returned a shipment of Bulgarian shoes for poor quality, western sources said.

These new economic strains have coincided with exceptionally bad weather and infrastructure breakdowns to produce a crunch far more severe than planners expected. Power plants broke down and factories ground to a halt during this year's severe winter, and a drought this summer badly damaged crops and reduced water supplies for both consumption and hydroelectric power.

The result has been a slump in industrial production and a severe energy shortage that the government so far has been unable to alleviate despite energy-saving programs in industry, forced cutbacks in public consumption and exceptional purchases of fuels such as coal on western markets. "What we have already achieved in energy conservation is not much," Stoilov said. "Considerable changes are needed."

Now, according to western diplomats, Sofia residents endure electricity cutoffs ranging from three to 12 hours a day, and stores operate on a special schedule of shortened hours to save energy. Newspaper articles have encouraged citizens to use wood rather than coal as fuel. Price rises in September included 35 percent for gasoline, 41 percent for household electricity and 66 percent for drinking water.

Though government economists cite the drought, bad weather and poor world economic conditions, the official press increasingly has put the blame on the state apparatus of planners and managers. In a recent editorial, the Communist Party newspaper Rabotnichesko Delo said planners had handled problems in "a common and routine" manner, allowing "inefficient use of raw materials and fodder."

Such attacks, combined with the evident Soviet displeasure, have spurred speculation in Sofia that the economic troubles may set the stage for a shakeup of government leadership. Zhivkov, though apparently healthy at 74, is now flanked by several technocrats in their fifties, including Prime Minister Georgi Filipov, Ognyan Doinov, the minister of machine building, and Chudomir Alexandrov, a new Politburo member recently named to head a government energy commission.

Some diplomats here believe that Zhivkov could become the first of Eastern Europe's aging leaders to step down as Soviet Bloc countries stage Communist Party congresses early next year. At the least, one European envoy said, "He will have to come to terms with Gorbachev. And it will not be as simple as it has been for Bulgaria before."