NEW YORK, July 15 (Reuters) - Freddie Mac (FRE.P: Quote, Profile, Research) said on Wednesday it sold a $1 billion reopening of an outstanding three-year note issue at a 1.770 percent rate, bringing the total size of the offering to $7 billion.

The issue, due June 15, 2012, was priced at 99.942 in an Internet auction, and drew 3.27 bids for every note sold.

This was the first of two issuance windows the second-largest U.S. home funding company has for reference notes in July. (Reporting by Lynn Adler; Editing by James Dalgleish)