* Hyundai Heavy offers 3.2 mln shares of Hyundai Motor in block deal
* Offering worth up to $636 mln would be S.Korea's biggest of 2012 (Adds details of the offering, South Korean equity deals, bookrunner)
HONG KONG/SEOUL, July 16 (Reuters) - Hyundai Heavy Industries hopes to raise up to $636 million selling a stake in Hyundai Motor, as the South Korean shipbuilder looks to improve its financial health in the country's biggest equity capital markets deal this year.
Hyundai Heavy is offering 3.2 million Hyundai Motor shares at 219,500-228,500 Korean won, equivalent to a discount of up to 3.9 percent on Monday's closing price, according to a source with direct knowledge of the plans.
At the top end of the range, Hyundai Heavy would raise about 731 billion Korean won ($636 billion), in South Korea's biggest stock offering since chemical producer KCC Corp sold a $602 million stake in Hyundai Heavy on Jan. 12.
Hyundai Heavy said in a regulatory filing the stake had a book value of 746.4 billion won at the end of the first quarter and the sale would improve its financial structure.
The block sale announcement came after Hyundai Heavy's share price fell 8 percent this month to hit its lowest closing price in more than two years on Monday on expectations second-quarter earnings will be hit by the fallout from Europe's debt crisis.
The move came after South Korean refiner Hyundai Oilbank, 91.1 percent owned by Hyundai Heavy, postponed a $2 billion initial public offering in June because of volatile markets and ahead of a suspension of Iran crude imports on western sanctions.
Hyundai Heavy will still hold a 2 percent stake in the automaker after the sale.
Citigroup was hired as sole bookrunner for the deal. ($1 = 1,150.30 Korean won) (Reporting by Elzio Barreto in Hong Kong, and Ju-min Park and Hyunjoo Jin in Seoul; Editing by Muralikumar Anantharaman and Dan Lalor)