The criteria we applied had evolved in the aftermath of the Libyan bombing of Pan American flight 103 over Lockerbie, when Congress held hearings to investigate charges that the U.S. government had known of the impending attack and failed to issue a warning.

Although these charges were unfounded, a useful standard evolved for deciding when to issue a public warning. Threat information had to meet three tests: It had to be specific; credible; and impossible to counter.

So if, for example, information from an intercept or an informant suggested the possibility of a plot to bomb Buckingham Palace, that would meet the first test, but depending on the source, perhaps not the second, and probably not the third, given the capabilities of MI5 and the Special Branch.

These decisions were sometimes very difficult, and reasonable people could disagree, often based on the nature of their responsibilities. Those in the intelligence business were reluctant to compromise sources and methods, while others tended to put the immediate safety of Americans first.

The bureaucratic course of least resistance was to make the threat public in a general way, while withholding the very information that would help people make prudent decisions. Whenever we could, we tried to ensure that the warnings we issued were actionable and as specific as possible.

In this case, the internal battle appears to have been won by those who were determined to tell Americans virtually nothing about the nature of the threat, and the State Department was left holding the bag.

I have no doubt that the intelligence which led to the Oct. 3 alert was disturbing, and that some of it was quite specific. The behavior of several European governments demonstrates that the risk of an attack was, and probably remains, real. And obviously it is important not to tip our hand to the terrorists.