On view are documents revealing secret exchanges about how to prevent Chile’s Congress from ratifying the Allende victory in 1970, plans for covert operations to destabilize his government and reports about a Chilean military officer informing the United States government of the coming coup and requesting assistance.

There is a cable from the Central Intelligence Agency to its officers in Santiago after a failed operation in October 1970 to prevent Allende from assuming office, which he did that November. The C.I.A. provided weapons for the plan, which resulted in the killing of the commander in chief of the army, Gen. René Schneider, and the agency later sent money to help some of the plotters flee the country.

“The station has done an excellent job of guiding Chileans to a point today where a military solution is at least an option for them,” the cable says, commending the officers, even though their plot was foiled.

The exhibition includes only a small sample of the 23,000 documents on Chile that the Clinton administration declassified between 1999 and 2000 in response to international requests for evidence on Pinochet’s crimes. The former Chilean dictator was arrested in London in October 1998 and awaited extradition to Spain to face trial on charges of human rights abuses during his rule.

As several other European countries also sought Pinochet’s extradition based on the principle of universal jurisdiction, Mr. Kornbluh, the curator, led a campaign to persuade the White House to release classified records that could serve in an eventual trial against the general.

Documents on Chile from 1968 to 1991 from seven United States government agencies, some of them heavily redacted, were released as part of the State Department’s Chile Declassification Project. Most were declassified months after Pinochet was sent home from London for humanitarian reasons, but just in time to contribute to new judicial investigations in Chile.