WASHINGTON — A wide-ranging surveillance operation by the Food and Drug Administration against a group of its own scientists used an enemies list of sorts as it secretly captured thousands of e-mails that the disgruntled scientists sent privately to members of Congress, lawyers, labor officials, journalists and even President Obama, previously undisclosed records show.

What began as a narrow investigation into the possible leaking of confidential agency information by five scientists quickly grew in mid-2010 into a much broader campaign to counter outside critics of the agency’s medical review process, according to the cache of more than 80,000 pages of computer documents generated by the surveillance effort.

Moving to quell what one memorandum called the “collaboration” of the F.D.A.’s opponents, the surveillance operation identified 21 agency employees, Congressional officials, outside medical researchers and journalists thought to be working together to put out negative and “defamatory” information about the agency.

F.D.A. officials defended the surveillance operation, saying that the computer monitoring was limited to the five scientists suspected of leaking confidential information about the safety and design of medical devices.