DUBAI, Oct 19 (Reuters) - Saudi Basic Industries helped lift Riyadh's stock market early on Wednesday after it reported a third-quarter net profit at the top end of forecasts, but a loss at Qatar's third- largest bank dragged that market lower.

Riyadh's stock index was up 0.4 percent after half an hour of trade.

SABIC, the Gulf's largest petrochemical producer, climbed 1.5 percent after posting a net profit of 5.22 billion riyals ($1.39 billion) in the three months to Sept. 30, down 6.8 percent from a year ago. Analysts polled by Reuters had on average predicted 5.05 billion riyals.

The company attributed the profit fall to lower average sales prices and a reduction in the quantity of products sold, outweighing benefits gained from a decrease in costs.

Roughly two-thirds of Saudi petrochemical producers have now reported third-quarter earnings, with generally weak results. Nama Chemicals , a mid-sized producer, said it made a wider loss in the third quarter of 32.6 million riyals versus a loss of 24.0 million riyals in the same period of 2015. Its shares were down 1.1 percent.

Emaar the Economic City , developer of an industrial city near Jeddah, dropped 1.6 percent after reporting a third-quarter net loss of 81 million riyals versus a profit of 8 million riyals a year ago.

Middle East Healthcare Co jumped 6.3 percent after its quarterly net income rose 1.4 percent to 92 million riyals.

In Qatar, the index pulled back 0.6 percent as Commercial Bank of Qatar slipped 4.6 percent. The bank made a net attributable loss of 1.04 million riyals ($285,612) in the third quarter versus a profit of 275.9 million riyals a year earlier; analysts polled by Reuters had forecast a profit of 281.7 million riyals.

The bank cited provisions for non-performing loans, after former Australia and New Zealand Banking Group banker Joseph Abraham was appointed chief executive in July.

Medicare Group sank 2.9 percent after reporting an 85 percent drop in third-quarter net profit to 4.8 million riyals.

Qatar Insurance was down 1.3 percent on a 6 percent fall in third-quarter profit to 108.8 million riyals, considerably below EFG Hermes' forecast of 312 million riyals.

In Dubai, the index was down 0.2 percent in quiet trade as no major companies posted fresh results. Dubai Investment lost 1.0 percent.

(Reporting by Celine Aswad; Editing by Andrew Torchia) ((celine.aswad@thomsonreuters.com)(+9715 62247653)(Reuters Messaging: celine.aswad.thomsonreuters.com@reuters.net))