CORRECTED-U.S. did not detail request for auto rules of origin at NAFTA talks -source

-source@ (Corrects to make clear United States did raise rules of origin, but did not give details)

WASHINGTON, Aug 19 (Reuters) - In the opening NAFTA session of talks, the United States did not give precise details of how much it wanted to boost North American content for autos, a source directly familiar with the negotiations said on Saturday.

A top U.S. official said on Wednesday that Washington wanted tougher rules of origin, which determine how much of an auto must be built in the three NAFTA nations, as well as new measures to ensure "substantial U.S. content" for autos. (Reporting by Anthony Esposito and David Ljunggren; Editing by Lisa Von Ahn)