WASHINGTON — The CIA pulled the veil back Wednesday on long-classified foreign intelligence briefings it gave President Richard Nixon in the 1970s during the height of his power and his fall from grace.

The release of 2,500 President's Daily Briefs — about 28,000 pages in all — shed light on such historic events as Nixon's opening to China, the invasion of Cambodia, the U.S.-backed overthrow of an elected leader in Chile, the 1973 Arab-Israeli war, and ultimately the first resignation of a sitting U.S. president.

The release also covers briefings given to President Gerald Ford, who took over when Nixon resigned on Aug. 9, 1974, until he left office in January 1977. That period included the fall of Saigon and the end of America's war in Vietnam.

CIA Director John Brennan and Director of National Intelligence James Clapper released the briefs and other documents at a symposium at the Richard Nixon Presidential Library in Yorba Linda, Calif.

Nixon relied on his national security adviser, Henry Kissinger, to forward the written summary and other material every morning, leaving CIA officials discouraged at their lack of access, according to a declassified 1996 agency history of the CIA-Nixon relationship, also released Wednesday

Other than in formal or ceremonial meetings, Nixon never met privately with the three CIA directors who served under him. He had only a single telephone conversation with William Colby, who headed the spy service during the resignation scandal.

“When you did brief him on something, he looked like his mind was on other things — he may have been thinking about Watergate, I guess,” Colby later told a CIA interviewer, according to the documents.

The CIA briefs ran about 10 pages a day and often contained mostly news items and mundane political analysis from hot spots around the globe, a useful service in the era before 24-hour cable news and the internet.

They contain several references to satellite surveillance and other high-tech intelligence gathering tools. But sensitive passages about covert operations and secrets stolen by undercover operatives are blacked out in the released documents.

The papers still contain fascinating tidbits.

Although Nixon publicly called his 1972 visit to China “the week that changed the world,” his four-page intelligence brief on the day of his arrival in Beijing contained only two paragraphs on the trip.

The material reveals how little the CIA's China watchers knew about the Communist leaders of the world's most populous country, then just emerging from more than two decades of isolation.

The following day, the CIA summary offered two paragraphs of analysis on reaction in the Soviet Union, which saw the prospect of closer relations between China and the U.S. as a threat.

“The Soviets are using their news media to cast President Nixon's visit to China in an unfavorable light,” the briefing read, noting that the Communist Party newspaper “characterized the trip as being predicated on common hatred for the Soviet Union.”

Developments in Indochina — where the U.S. was trying to extricate itself from the war in Vietnam and prop up failing governments in neighboring Cambodia and Laos — received intense attention in Nixon's daily intelligence summaries. A brief item on Feb. 4, 1974, reveals that even minute details about Cambodia's communist rebels, known as the Khmer Rouge, gleaned from U.S. intelligence eavesdropping operations, were being forwarded to the White House.

“An intercept of February 1 indicates that a meeting of the standing committee of the Khmer Communist Party is being called for February 5 or 6 at an undisclosed location,” the summary reported.

david.cloud@latimes.com