* U.S. government shutdown keeps buyers on sidelines -dealers

* Fiber heads toward biggest one-week drop since August

* Uncertainty prevails with key U.S. government reports absent

By Marina Lopes

NEW YORK, Oct 10 (Reuters) - Cotton futures eased to a fifth consecutive loss on Thursday, hovering near the previous session's one-month low as the second week of a U.S. government shutdown held buyers on the sidelines.

The most-active December cotton contract on ICE Futures U.S. fell 0.03 cent, or 0.04 percent, to settle at 83.17 cents a lb.

Prices hovered near the previous session's four-week low of 83.10 cents a lb.

The contract is on track for its biggest weekly fall since August.

Cotton underperformed the broader commodity market, as the Thomson Reuters-Jefferies CRB index gained.

Equities rallied on Thursday, with major stock indexes up on signs of progress in negotiations to raise the U.S. debt limit, and the dollar rose to a two-week high.

"The market is hardly moving, we are just holding our breath to see if the politicians can affect some type of deal to end this shutdown," said Keith Brown, president of commodity firm Keith Brown and Co in Moultrie, Georgia.

The government standstill has kept pressure on fiber after prices slid at the start of the week. Concerns over Tropical Storm Karen lifted cotton to a six-week high last week.

The storm weakened over the weekend and left crops in key growing regions of the United States, the world's top exporter, largely unscathed.

A prolonged government shutdown could hamper farmers' access to crucial federal loans and has denied traders access to key government statistics, like the monthly crop report which was scheduled to be released on Friday.

"Lack of the USDA report creates a Catch-22 because you could do nothing and have no volatility, or you could have hyper volatility, as we saw in the day after the shutdown," said Sharon Johnson, a cotton specialist at KCG Futures in Atlanta.

Exchange stocks climbed again, rising to over 17,000 bales from below 15,000 bales the previous session, the most recent ICE data showed.

Nearly 39,000 bales were awaiting review.

An uptick in certified stocks has pushed the December contract to a discount to the March contract this week for the first time since May.

The December contract had been trading at a premium as a steep drop in exchange stocks and crop worries stoked concern over tight nearby supplies in the United States. (Editing by Jim Marshall)