* Managed money net longs at $70 bln vs $67 bln year ago
* Crude oil open interest down from $8 bln to $1.3 bln
* Changes due to price moves, shift in trading positions
* Global macro trends seen lending more volatility in 2013
By Barani Krishnan
Jan 4 (Reuters) - Hedge funds and other big speculators held just over $70 billion worth of bullish bets on U.S. commodities as the year began, barely changed from 12 months ago, after two weak quarters offset price gains from the rest of 2012, data showed.
Holdings in oil saw some of the most dramatic shifts in value over the year. Open interest in U.S. crude held by money managers fell from 77,717 lots worth about $8 billion to just around 13,391 lots valued at less than $1.3 billion, according to data from the U.S. Commodity Futures Trading Commission.
Total value of all net long contracts in U.S. commodity futures under the so-called "managed money" classification stood at $70.4 billion on Jan. 1, versus $66.8 billion on Jan. 3, 2012, CFTC figures compiled and calculated by Reuters showed.
The change in value was subject to price movements as well shift in trading positions.
Commodity markets saw particularly volatile moves in 2012, starting the year strong before being depressed in the second quarter by Europe's debt crisis.
Prices rebounded in the third quarter, with grains markets especially buoyed by the worst U.S. drought in half a century. But as the final quarter beckoned, markets resumed their downtrend on worries over China's slowing economy and a fiscal crisis in the United States.
"The phenomenal ups and downs in the CFTC data shows investors are still concerned with the broader global macro threats which constantly affect commodity prices," said Adam Sarhan at New York's Sarhan Capital.
While tentative signs have emerged that the euro zone economy could have passed the worst of its downturn, a recovery still looks some months away, a business survey issued this week by influential survey compiler Markit showed.
In the United States, many lawmakers and their aides fear things may get more toxic through a series of bitter struggles expected in the next few months over the nation's debt and deficit burdens. At stake is the U.S. government's ability to get its finances under control and whether it might default on debts and suffer further downgrades in the U.S. credit rating.
Some commodities showed strong builds in net long positions as the new year began, while others exhibited heavier bets on the short side that pressured prices.
The net long position in cotton held by money managers rose for a fourth straight week.
In natural gas, hedge funds and speculators cut net longs for a fifth week running.