Beijing ? The CIA is offering a rare glimpse into its successes and failures at trying to understand China during its first communist decades in a huge cache of newly declassified documents released this week in Washington.

The group of 71 intelligence reports covers three decades until 1976, the year communist founder Mao Zedong died. They reflect the U.S. intelligence agency’s struggle to track China’s political and economic evolution, its rise as a military power and its break with its former Soviet patrons.

“The documents in this volume played an essential role in helping U.S. government leaders and officials formulate policy toward” China after the 1949 revolution, Robert Suettinger, a former intelligence analyst, wrote in an introduction to the collection.

“They are, in a sense, some of the foundation stones for a work that is still in progress.”

The CIA says the reports, which include high-level National Intelligence Estimates, are the biggest single batch of declassified agency documents ever released.

They indicate that despite occasional missteps, assessments often were generally accurate. They included the conclusion that the Communist Party faced no serious challenges to its control, despite American support for Taiwan’s rival Nationalists, which fled the mainland in 1949 after losing a civil war and hoped to return to power.

And despite conflicting signals during the chaos of the ultra-radical 1966-76 Cultural Revolution, they also foresaw that moderate political and military leaders would emerge to take power.

However, occasional mistakes also are revealed as the analysts tried to follow the secretive Beijing government, relying on Hong Kong press reports, interviews with ethnic Chinese who had visited relatives on the mainland, and other secondhand sources.

As China prepared to explode its first nuclear bomb, the CIA was aware of the preparations, but thought the country hadn’t produced enough fissionable material for a test before the end of 1964. China set off its first explosion Oct. 16, 1964.

The CIA also initially underestimated the scale and importance of the Sino-Soviet split — the souring of Beijing’s relations with its former patrons in Moscow that began in the 1950s.

Analysts said in 1966 that an open break was unlikely. Three years later, the rancor erupted into bloody border clashes.

The reports show another miscalculation by analysts, who relied on falsified statistics while forecasting China’s economic outlook in the late 1950s. It is a problem Chinese leaders even today complain about — phony economic figures made up by low-level officials eager to make themselves look good.

While expressing skepticism at some numbers, the analysts nonetheless issued an upbeat economic outlook in the late 1950s.

In reality, the country was sliding toward disaster. The Great Leap Forward, an attempt at rapid industrialization, was on the brink of failure. The country fell into a slump that would cause as many as 30 million deaths from famine in 1959-61.

Some reports can sound eerily contemporary.

A 1961 document says Beijing “will continue its refusal to renounce the use of force for the seizure of Taiwan” — a position that the mainland government espouses today.

“But,” the report said, “we believe that concern over retaliation by the U.S. will deter it from attempting a military conquest of Taiwan.”