* Offering U.S. Treasury interest rate futures

* Backed by 13 banks and other financial firms

* Success seen as long shot

By Jonathan Spicer

NEW YORK, July 10 (Reuters) - U.S. futures exchange ELX Futures LP launches on Friday, challenging derivatives giant CME Group Inc (CME.O: Quote, Profile, Research) with the backing of its bank owners and an introductory offer of free trading this month.

ELX will first offer trading in U.S. Treasury interest rate futures, and hopes to expand its product suite in the future.

Analysts see ELX's success as a long shot, given Chicago-based CME's deep liquidity in Treasury futures and its ability to adjust prices to fend off rivals. But New York-based ELX has turned heads in the last few months, announcing a flurry of agreements ahead of its launch.

Goldman Sachs (GS.N: Quote, Profile, Research) on June 1 brought to 13 the number of banks and other firms in ELX's consortium of founding partners. Others include JPMorgan (JPM.N: Quote, Profile, Research), Bank of America (BAC.N: Quote, Profile, Research), Deutsche Bank (DBKGn.DE: Quote, Profile, Research) and big market maker GETCO.

In the last two weeks, commodity futures broker MF Global Ltd (MF.N: Quote, Profile, Research) and derivatives broker Newedge signed on as merchants for ELX products.