Fannie, Freddie shares dive, banks stocks weaken

* Fannie, Freddie shares fall on shareholder concerns

* Credit fears batter global banking stocks

* Bernanke testimony eyed

By Steven C. Johnson

NEW YORK, July 15 (Reuters) - Investors unloaded shares of Fannie Mae (FNM.N: Quote, Profile, Research) and Freddie Mac (FRE.N: Quote, Profile, Research) on Tuesday amid mounting concern that a government rescue plan for the two U.S. mortgage finance giants could hurt existing shareholders.

Banking stocks also tumbled, led lower by US Bancorp (USB.N: Quote, Profile, Research) and Wachovia Corp (WB.N: Quote, Profile, Research), as fears about fresh credit losses curbed investor appetite for financial shares.

Fannie shares plunged 18 percent after the opening bell to $7.98 while shares of Freddie Mac declined 22.6 percent to $5.49. Analysts said markets were worried about what the government's pledged support for the nation's top mortgage finance agencies would mean for the firms' shareholders.

U.S. agency note risk premiums widened by 2 to 5 basis points in early trading as the sector underperformed a bounce in Treasuries prices on safe-haven buying as stocks slid.