A Defense Intelligence Agency study unveiled yesterday con-cludes that the Soviet Union's energy reserves are more valuable than previously estimated, but cannot compensate fully for the detrimental effect on the economy of high military spending.

The report also highlights growing discontent and low morale in the Chinese armed forces, which it says could jeopardize the stability of the ruling Communist Party leadership.

The study contradicts past predictions by the Central Intelligence Agency that the Soviets would face an oil shortage in the 1990s, and also forecasts that their natural gas production will continue to rise and will soon exceed the rest of the world's production.

But the DIA analysis, given to the Congressional Joint Economic Committee in July and released yesterday, suggests that Soviet economic growth will continue to be "very slow," partly because the leadership has opted for continued growth in defense spending over the next five years despite a stagnant standard of living, high inflation and a lack of certain raw materials.

The report says: "Soviet leaders face difficult choices in this environment: a continued high priority for military power conflicts directly with securing economic growth at rates that will fulfill both domestic and foreign resources requirements."

One drain on the economy described in the report is the cost of maintaining "client" states: Soviet aid to other Communist countries rose from nearly $2 billion in 1971 to a startling $24 billion in 1980, including military aid, subsidies on oil exports to Eastern Europe and on such imports as sugar from Cuba.

DIA deputy director Richard X. Larkin and vice director for foreign intelligence Edward M. Collins told the committee that the "unprecedented degree of Soviet forbearance toward Poland" can be explained by the potentially fatal effect of Polish resistance and economic disturbance to the Council for Mutual Economic Assistance, intended to be the Eastern Bloc's answer to the European Economic Community.

On energy, however, the outlook is said to be "highly favorable" for the Soviets, with oil production expected to rise above 12 million barrels a day, leveling off in the late 1980s and starting to rise again in the 1990s. Part of the reason is the expected start of production in five or six years at the "very large" Salym field in Siberia; the field is equivalent in area to the eastern half of the United States.

The DIA concludes that the Soviet Union will remain a net oil exporter for the foreseeable future, and that in 1985 hard currency earnings will reach $11.4 billion from oil exports and $11.2 billion from gas exports.

The report assumes that the planned gas pipeline from Siberia to western Europe -- which is being opposed by the Reagan administration -- will go ahead, and is likely to result in greater political influence for the Soviet Union in western Europe. Potential customers include West Germany, France and Italy, who are expected to receive gas worth about $10 billion annually through the pipeline.

On defense spending, the DIA notes that Soviets have indicated a strong response to planned increases in U.S. allocations. "The Soviets are prepared to allocate substantial additional resources to the military, with full recognition of the harm to the economy, if Soviet national security, in their perception, is threatened," the report says.

It also analyzes military developments in China, and suggests that close attention be paid to "significant" discontent in the People's Liberation Army, caused by low wages, a lower military budget and opposition in the forces to the continued criticism of the late Chairman Mao Tse-tung.

The report says: "There is a possibility that discontent in the military hierarchy will increase and the military may become more active in the decision-making process. If this occurs, military-party relations could reach the point where party leadership stability is jeopardized."

Morale has been damaged by the lower priority given to the military in the current economic modernization program, according to the DIA, and military leaders who have acquiesced in the plan in the hope that it will produce a stronger economy, allowing increased allocations for the army, may become more actively involved in the political and economic decision-making process if it fails.