Seoul shares up 0.8 pct on shipyards, Samsung Elec

* KOSPI rises 0.8 pct helped by U.S. GDP data, foreign buying

* Samsung Electronics gains after Q3 results; caution on Q4

* Shipbuilders rally after losses; Daewoo up on order hopes (Updates to mid-morning)

By Jungyoun Park

SEOUL, Oct 30 (Reuters) - Seoul shares rose on Friday, but trimmed its earlier opening gains of 1.2 percent weighed by falls in automakers including Hyundai Motor (005380.KS), but shipbuilders' rallies helped lend support to markets.

Analysts said positive U.S. gross domestic product (GDP) data and share gains on Wall Street helped lift Seoul stocks but sentiment remained relatively weak.

"The index fell below its 60-day moving average yesterday and I think that shook investors pretty hard...sentiment still remains weak," said Kwak Joong-bo, a market analyst at Hana Daetoo Securities.

The main KOSPI index's 60-day moving average is about 1,600 points, Thomson Reuters I/B/E/S showed.

The Korea Composite Stock Price Index (KOSPI) was up 0.77 percent at 1,598.10 points as of 0220 GMT.

Samsung Electronics (005930.KS) rose 2 percent after the world's No.1 memory chip maker reported record quarterly net profits. [ID:nSEO293078]

But shares were volatile during the earlier session, slashing its gains to as low as 0.56 percent, amid concerns its earnings momentum will weaken in the fourth quarter.

"Samsung is already entering a down cycle. Its memory chip unit will probably continue to do well in the fourth quarter, but LCD and handset units will see their earnings momentum growing weak," said Park Hyun, an analyst at Prudential Investment & Securities, adding that "momentum will probably weaken through the first quarter of next year."

Park added that the won's KRW strength was one of the key risk factors.

But shipbuilders rose across the board, with Daewoo Shipbuilding & Marine Engineering (042660.KS) leading gains on market talk it was likely to win a $300 million order from Angolian state-owned oil firm Sonangol for five tankers.

A source with knowledge of the deal confirmed with Reuters the South Korean shipbuilder was in talks with the Angolian company.

"There was talk early this morning Daewoo Shipbuilding may be winning the Angola order, and this is an added help to its shares," said Cho In-karp, an analyst at Shinhan Investment Corp.