UPDATE 1-Samsung SDI Q3 profit beats fcast on battery strength

* Q3 operating profit beats f'casts, up 10 pct vs year ago

* Expects battery, plasma panel demand to continue rising

* Shares down 0.4 pct; have more than doubled year to date (Adds details)

SEOUL, Oct 20 (Reuters) - Samsung SDI (006400.KS) posted a better-than-expected quarterly operating profit on Tuesday, helped by robust growth in rechargeable battery sales and narrowing losses from its plasma panel business.

While the short-term profit momentum is limited due to its unprofitable plasma business and competition in lithium-ion batteries, the South Korean company is set to become a key beneficiary of future growth in electric car batteries and new organic displays for smartphones.

Its shares fell 0.35 percent as of 0506 GMT, compared with the wider market's .KS11 0.52 percent gain. The stock has more than doubled this year, leading the KOSPI's 47 percent advance.

Samsung SDI expected demand for lithium ion batteries, used in mobile phones and notebook PCs, to grow 12 percent in the fourth quarter from the third, led by seasonal strength in notebook computers.

Global plasma panel demand is likely to increase 13 percent in the October-December period, the company said in a statement.

Samsung SDI reported an 88.1 billion won ($75.5 million) operating profit in the third quarter to September, above a 66.3 billion won profit forecast by analysts polled by Thomson Reuters I/B/E/S.

The consolidated-basis result rose from operating profits of 80.1 billion won a year earlier and 48.4 billion won in the second quarter, and marked a sharp improvement from a 76 billion won operating loss in January-March.

Quarterly net profit came at 87 billion won, also larger than a forecast of 74.8 billion won.

Consolidated sales were 1.35 trillion won, roughly in line with forecasts.

Shipments of batteries are rising at a fast clip but competition with Japanese rivals such as Sanyo Electric 6764.T are pressuring margins at Samsung SDI.

Its plasma panel business, now managed by Samsung Electronics (005930.KS), has suffered narrowing but continued losses as rival liquid crystal display (LCD) technology dominates the market.

For mobile phone screens, Samsung SDI runs an equal venture with Samsung Electronics named Samsung Mobile Display. It also operates the automobile battery unit jointly with Germany's Robert Bosch [ROBG.UL]. (Reporting by Rhee So-eui; Editing by Jonathan Hopfner)