* Long commodity index holdings at $284.1 bln
* Excluding short positions, net holdings up by $6.8 bln
July 30 (Reuters) - Investment in commodity indexes rose in June, snapping a three-month decline, as renewed hopes for a solution to the euro zone crisis boosted most risk assets, figures from the U.S. Commodity Futures Trading Commission showed on Monday.
In its first monthly data showing an uptick in commodity market positions since February, the CFTC said the value of net long index investments rose by $6.8 billion, or nearly 4 percent, to $190.8 billion in June.
The notional value of long-only index investments -- representing bets for higher prices -- stood at $284.1 billion in June versus $269.9 billion in May, the CFTC reported.
Short-only positions -- or bets that prices will fall -- also rose, but much less than the long-only investments, reaching $93.9 billion in June versus $85.9 billion in May.
The previous rise in net-long investments noted by the CFTC was in February, when the tally went to $209.9 from January's $196.9 billion.
June marked a watershed moment for commodities, with oil prices jumping nearly 10 percent on the last session of the month after the European Union surprised markets by announcing measures to cut borrowing costs for Greece and Spain after a long period of no progress in the region's debt crisis.
The Thomson Reuters-Jefferies CRB index, the commodity market bellwether, had fallen by about 16 percent from March through May as prices declined steadily from a selloff by investors worried about the euro zone crisis and the global economic climate.
In June, the index rose 4 percent and is poised to end July up by more than 6 percent for its best month since October.
The CFTC data does not calculate the estimated in-flow or out-flow from markets, only the value of index-based futures positions at the end of month.
If sustained, the surge in confidence among index investors, who are typically long-term buyers, could be a positive trend for commodity traders, who have come to count on a steady stream of fresh capital flowing into markets. Total net assets have swollen from nearly nil to some $400 billion in a decade.