UPDATE 2-Boeing doubles 787 deliveries in the third quarter

(Adds 787 background, analyst comment)

Oct 4 (Reuters) - Boeing Co said on Thursday it doubled deliveries of its fuel-efficient 787 jets in the third quarter to 12, compared with six in the second quarter.

Boeing is years behind its initial delivery schedule on the new light-weight, carbon-composite 787 aircraft after extensive development delays.

The company declined to say how many of the 787s delivered in the quarter came from a group of previously produced jets that needed engineering changes after they left the factory.

Boeing has produced more than 70 of its 787 jet and delivered 26, suggesting that 45 or more jets require the post-factory retrofitting, said Russell Solomon an analyst at Moody's Investors Service in New York.

"When you do the math, there are 50-ish sitting there with some level of work that needs to be completed," he said. "We think most of those will get delivered next year. A few more from that group should be delivered this year."

All of 787s delivered so far have been produced at Boeing's plant in Everett, Wash.

Boeing is trying to speed up production to five 787s per month by year-end. The rate will include jets made at its plant in South Carolina. That factory is expected to deliver its first 787 from South Carolina on Friday, to Air India.

Overall, the company delivered 149 jets in the third quarter, down from 150 in the second, but up from 137 in the first quarter. Deliveries rose 17 percent from a year ago.

Orders rose sharply in the latest quarter, hitting 404, compared with 36 in the second quarter.

Orders for the new 737 MAX drove the increase, Boeing said. The company logged orders for 377 of the single-aisle 737 jets in the quarter, up from just three in the second quarter of 2012, and compared with 243 in the third quarter of 2011.

Among the big buyers, United Airlines ordered 100 of the 737 MAX planes, and Air Lease Corp and GE Capital Aviation Services ordered 75 each. Virgin Australia Airlines ordered 23.

(Reporting by Alwyn Scott; Editing by Maureen Bavdek, Tim Dobbyn and M.D. Golan)