Two other incidents in Houston in November and in San Diego in July involved clay and, in one case, a battery and wires, the report said.
"I'd like to see more bulletins of this type coming out of the Department" of Homeland Security, Rollins said, noting that the department was not producing such in-depth reports in areas like rail security or food safety.
Other security experts, however wondered whether the devices described in the report could really be the work of terrorists.
"Part of my puzzlement is, these seem like really crude devices," said Gerald Epstein, a homeland security specialist at the Center for Strategic and International Studies in Washington. "I think there are terrorists out there who could build something much less like what you would find in a comic strip."
The size of the devices mentioned in the report suggested a lack of terrorist savvy, said Brian Jenkins, an aviation security specialist at the Rand Corp. think tank.
Romero said, however, that the combinations of items did not strike him as rudimentary and that terrorists testing a detection system might use quantities larger than what they would use during an actual attack to gauge the limits of the government's ability to screen for explosives.
News of the intelligence report also reignited a debate over how much threat information should be released to the public.
Some counterterrorism officials complained that publicizing a report that highlighted one possible threat had diverted government officials away from their security responsibilities in order to deal with a public relations problem.
Former officials said, however, that since such reports are unclassified, they should be released routinely as a way of enhancing the public's understanding of possible terrorist threats.
siobhan.gorman@baltsun.com
Sun reporters Meredith Cohn and Andrew Green contributed to this article.
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