COMMODITIES-Brutal start to August as key index hits 2003 lows

* Chart of China PMI vs GDP: http://link.reuters.com/huv55t (Adds analysts' comments, background; updates prices)

NEW YORK/LONDON, Aug 3 (Reuters) - A key global commodities price benchmark sank to 12-year lows on Monday as copper and sugar prices hit fresh multi-year lows and oil fell below $50 for the first time in six months, as fears about a hard economic landing in China and global glut deepened.

Selling by speculators intensified, getting August off to a brutal start, after data showed conditions for Chinese manufacturers deteriorated to their weakest in two years and U.S. factory data disappointed.

U.S. oil was also hit by expectations of weaker U.S. gasoline consumption after robust demand earlier in the summer.

Brent crude oil touched a low of $50.85 a barrel, its weakest since Jan. 30, after fresh evidence of growing oversupply.

"Weak Chinese data and (the) Iranian braggadocio about 500,000 additional barrels on the market as soon as sanctions are lifted (are) bruising already weak sentiment," said Tai Wong, director of base and precious metals trading for BMO Capital Markets in New York.

The 19-commodity Thomson Reuters (Dusseldorf: TOC.DU - news) /Core Commodity CRB Index , which has fallen 15 percent this year, hit its lowest since May 2003, with only four markets in positive territory.

The selling pushed oil, copper and sugar deeper into bear territory and reinforced concerns that the decade-long supercycle that has bolstered prices of everything from copper to crude fueled China's economic slowdown is petering out.

Equities also finished lower and the resource-linked Canadian dollar was at its weakest in more than a decade against its U.S. peer as crude prices sank.

Growth in the U.S. manufacturing sector slowed more than expected in July, while factory activity in China, the world's second-biggest economy, shrank more than estimated last month.

A Reuters survey last week showed oil output by the Organization of the Petroleum Exporting Countries (OPEC) reached the highest monthly level in recent history in July.

"The market seems to again focus on the supply situation. ... One of the difficulties is that Iran may be coming back and there is no obvious sign that OPEC will make room for them," Ric Spooner, chief market analyst at CMC Markets in Sydney, said.

Benchmark copper on the London Metal Exchange dropped 1.7 percent to $5,142 a tonne, its lowest since July 2009, before paring losses.

China accounts for nearly half of global consumption of the metal used in power and construction.

Raw sugar hit a fresh 6-1/2-year low, pressured by a weaker Brazilian real currency and hefty stocks in India and Thailand.

Benchmark raw sugar futures settled down 0.25 cent, or 2.2 percent, at 10.89 cents a lb, after falling to 10.84 cents, the lowest since December 2008.

Gold was relatively calm, as the dollar steadied ahead of U.S. economic indicators that could bolster expectations for a rise in U.S. interest rates soon.

Spot gold, which fell by the most in two years in July, dipped 0.83 percent to $1,087.1 an ounce. (Reporting by Josephine Mason and Barani Krishnan in New York, Eric Onstad, Amanda Cooper, Pratima Desai, Clara Denina, David Brough and Mariana Ionova; Editing by David Evans and Richard Chang)