* Down 2nd day in row and bucking broad commods rally
* Traders positioning before weekly exports, Jan USDA data
NEW YORK Feb 5 (Reuters) - U.S cotton fell for a second straight day on Tuesday despite gains in other commodities, as investors refrained from buying at prices inflated by January's sharp gains as the market awaited export data and a government crop report due this week.
The most-active March cotton contract on ICE Futures U.S. settled down 23 cents, or 0.3 percent, at 81.51 cents per lb. In Monday's session, the contract fell 1.5 percent.
Cotton prices surged more than 10 percent in January.
Oil and most other commodities rose, buoyed by a survey showing business optimism in the euro zone at an eight-month high. U.S. data also pointed to growth in the services sector for January.
Market sources said cotton traders seemed to be positioning themselves ahead of Thursday's weekly exports data and Friday's January crop report from the U.S. Department of Agriculture (USDA).
"The export numbers are crucial, especially if they point to another cancellation in Chinese buying like in the previous week," said Keith Brown of commodity brokers Keith Brown & Co. in Multrie, Georgia.
"Everyone's also looking out for the USDA report, which will tell you where the crop and production estimates are at the moment."
Export numbers issued by the U.S. government last week indicated a decrease in exports of cotton from the prior week. It also marked the first time since mid-July that Chinese buyers had canceled orders for U.S. bales.
The USDA will report on the country's cotton supply and demand, aside from the crop situation for January. Prices rose last month after the agency cut its outlook for production, even though it raised its global surplus estimates for cotton.
Last Friday, figures from the U.S. Commodity Futures Trading Commission showed hedge funds and other speculative investors holding their largest net long position in cotton in more than two years.
The CFTC data contrasted somewhat with this week's selling pressure in cotton.
Some attributed the near 2 percent decline in the past two sessions to a recent uptick in cotton supply onto the ICE exchange. Over 52,000 480-lb bales are awaiting USDA approval now, compared to about 5,000 bales at the start of the year, ICE data shows.
The new supply is in addition to the already 146,990 bales registered with the exchange as of Feb. 4. In October, there were just about 8,000 bales registered. (Reporting by Barani Krishnan; Editing by David Gregorio)