(Adds terms of agreement, Samsung sale, JV earnings)
SEOUL, June 16 (Reuters) - Defence firm Samsung Techwin Co Ltd on Tuesday said it will sign an agreement giving it an option to buy Thales SA's 50 percent stake in their unlisted South Korean joint venture, valued at about $190 million.
The deal comes ahead of Samsung Group's expected sale later this month of stakes in Samsung Techwin and the joint venture, Samsung Thales Co Ltd, to Hanwha Group as part of a restructuring at South Korea's largest conglomerate.
The option agreement will allow Hanwha and French defence electronics group Thales time to try their partnership out before deciding to dissolve it or continue.
Samsung Techwin holds 50 percent of Samsung Thales.
According to the terms of the agreement, Thales has the right to sell its stake in the joint venture to a Hanwha unit in about a year after Hanwha Corp acquires Techwin.
Techwin also has the right to buy Thales' stake if the French company does not offer to sell first.
Thales' stake has a book value of 208.13 billion won ($186.16 million), according to a Samsung Techwin filing.
Samsung Thales, which makes digital defence systems, reported revenue of 678.4 billion won and operating profit of 26 billion won in 2014. ($1 = 1,118.0000 won) (Reporting by Joyce Lee; Editing by Stephen Coates)