* Dec-March spread widens, but carry still elusive

* Goldman Sachs index roll starts Wednesday

* Activity low across commodities ahead of U.S. election

NEW YORK, Nov 5 (Reuters) - U.S. cotton futures fell below 70 cents before recovering ground to settle slightly higher on Monday as the market braced for a major index roll later in the week.

"Cotton continues to drift sideways at the bottom of the recent range. Momentum seems to have stalled on the downside," said INTL FCStone market analysts in a report on Monday.

The most-active December cotton contract on ICE Futures U.S. settled up 0.05 cent at 70.40 cents per lb, after trading in a narrow range of less than 1 cent. Prices defied weaker grains and softs markets.

Technically, the market has weakened after December prices breached the psychologically key 70-cent mark for a fourth straight session. Prices are likely to remain under all the main moving averages in the short term, with support seen at 69.40 cents per lb, traders said.

Even so, there could be a brief pop higher after speculative investors cut their bullish bets by a third last week by increasing their short positions, traders said. Weak supply-and-demand fundamentals show no signs of improving.

"Everyone's sold everything they have to sell for now, so we might get a pop up to 72 cents again," said a Texas-based trader.

As is typical during the U.S. harvest, exchange certified cotton stocks rose for the ninth straight day, inching up 474 bales to 12,238 on Nov. 2, ICE data showed.

While that is its highest level since Oct. 1, inventory levels are well below a year ago when there were 35,000 bales in stock.

ROLLING

Pressure has built on the December as index funds roll their long positions by buying March and selling the front-end contract. The rolls kicked off at the end of October, with Goldman Sachs, the main index, due to start on Wednesday.

The front-month selling has increased the contango although it is still below a full carry which has eluded the market since October 2009, before the market was gripped by a deficit and prices started their year-long rally to records above $2 last March.

The March contract settled at 71.65, up 0.30 percent, leaving the spread between December and March at 1.25 cents.

The March price needs to be between 2 and 2.5 cents per lb above December to be at full carry, meaning it covers cost of holding the commodity until delivery.

Trading activity was low across the commodities market with few investors opening new positions ahead of the U.S. presidential election on Tuesday. Volume was 15 percent below the 30-day average, preliminary Thomson Reuters data showed.

More than half of the just under 20,000 lots that changed hands was in the December contract.