The proposal by the U.S. government to use RFID for passports has raised not only the usual concerns about privacy but a more troubling concern that such documents might make U.S. citizens targets in certain parts of the world.

Does this proposal, which is designed to reduce the risk to U.S. citizens in this country, actually endanger them in other countries?

On the surface, it's a plausible concern.  RFID tags, even if they have only a limited range, could be excited by a hidden reader.  In theory, terrorists would not even have to be able to read any of the information on the tag -- all they'd have to do is get a response to know that the individual is carrying a U.S. passport.

The idea behind RFID-enabled travel documents (U.S. passports, pilots' licenses, US-VISIT cards, trusted flyer cards, etc.) is to enable immigration officials to compare the biometric information encoded on the tag with the person presenting the document.  RFID will also provide more of an authenticity check for the document than would an optical symbol.

Data on the RFID tag would be automatically transmitted to a checkpoint computer.  The use of an optical symbol or laser card would require an official to manually scan the data (whether with a fixed location or insertion style reader). RFID would speed processing of individuals through checkpoints and allow officials more time to focus on suspicious or questionable individuals or documents.

However, insofar as RFID-enabled documents are designed for non-contact reading, does that immediately make them a handy tool for terrorists to target U.S. citizens?

There's a simple solution to this concern.  Place the RFID tag on the inside of the passport and embed a thin foil sheet in the cover.  This would block radio signals and make the tag invisible (non-response) to covert reading.  Opening the passport would enable the tag to be read.