As the misguided war in Iraq made clear, intelligence analysis is an uncertain game, all too vulnerable to error and politically motivated distortion. That experience has done little to change the intelligence community’s passion for secrets, whether or not they need to be kept.

Three decades later, we still do not know for certain — but have good reason to believe — that flawed or distorted intelligence led the Reagan administration to accuse the Soviet Union and Vietnam of using chemical weapons, known as yellow rain.

A classified critique of the intelligence behind those charges, written several years ago for the Central Intelligence Agency, could shed light on what happened. Last year, Matthew Meselson, a Harvard expert on chemical and biological weapons, filed a Freedom of Information Act request to get the report released. He was turned down. The report should be made public both for its historical value and its possible lessons on how to handle the challenge of divining an enemy’s capabilities and intentions.

In 1981 and 1982, the Reagan administration charged that the Soviet Union had supplied toxins made from a poisonous fungus to its Vietnamese and Laotian allies to use as a weapon against Hmong villagers who had sided with the United States during the Vietnam War and against anti-Vietnamese forces in Cambodia.