UPDATE 2-Asia Crude-India ONGC tenders for 1 Sokol lot for Sept

(Adds details of the September tender)

NEW DELHI, July 9 (Reuters) - India's Oil and Natural Gas Corp (ONGC) (ONGC.BO: Quote, Profile, Research) will sell only 700,000 barrels of Sokol crude for September loading, as output from the Sakhalin-1 field is falling, a company official said on Wednesday.

ONGC is offering one cargo of Sokol for loading around Sept. 16, tender documents show, after it also sold just one parcel for August lifting.

Before that, state-run ONGC has regularly sold two 700,000-barrel cargoes a month of the light sweet grade via tenders since October 2006.

"Production is declining. It is a natural decline... For September loading, there will be only one cargo for OVL," Anupam Mathur, commercial director at the firm's overseas investment arm, ONGC Videsh Ltd (OVL), told Reuters.

The latest tender closes on July 16, with bids to remain valid until July 17.

Production on the field, operated by U.S. major ExxonMobil (XOM.N: Quote, Profile, Research), peaked briefly at 250,000 barrels per day (bpd) last year but is expected to fall to 160,000-165,000 bpd this year.

Mathur said ONGC would decide by end-July, or early next month, on the number of cargoes for October lifting.

ONGC holds a 20 percent stake in Sakhalin-1.