FARNBOROUGH, England, July 22 (Reuters) - Boeing ( BA )

is set to announce on Monday an order for roughly 20 777X jets

from Korean Air, in a boost to the U.S. planemaker's

long-delayed plane programme, two sources familiar with the

matter said.

Reuters first reported the deal earlier in July. Monday's

announcement at the Farnborough Airshow could also include 787

jets, one of the sources said.

Boeing ( BA ) declined to comment.

South Korea's largest carrier has been in talks over a

potential return to its traditional supplier of long-haul

aircraft for months after placing a surprise order for 33 A350

jets from Airbus in March.

The 777X jets are worth some $198 million each after typical

discounts, according to delivery prices from Cirium Ascend.