UPDATE 1-ACE forecasts 2013 profit below estimates; shares drop

* Expects 2013 oper profit of $6.60-$7.00/shr vs est $7.89

* 4th-qtr operating profit $1.43 vs $1.90 a year earlier

* After-tax catastrophe losses triple to $400 million

* Shares fall 5 pct in extended trading

Jan 29 (Reuters) - Insurer ACE Ltd reported a 24 percent fall in quarterly operating profit, hurt by losses related to superstorm Sandy, and forecast a full-year profit below analysts' estimates.

After-tax catastrophe losses tripled to $400 million in the fourth quarter from $137 million a year earlier. The insurer took a loss of $393 million resulting from Sandy, marginally higher than the $380 million it estimated in December.

ACE's shares were down 5 percent in extended trading after closing at $84.94 on Tuesday on the New York Stock Exchange.

The company forecast an operating profit of between $6.60 and $7.00 per share for 2013, below the average analyst forecast of $7.89 per share.

ACE projected catastrophe losses of $395 million after tax for 2013.

Net earnings rose to $765 million, or $2.22 per share, for the fourth quarter, from $735 million, or $2.15 per share, a year earlier.

On an operating basis, the Zurich-based property and casualty insurer and reinsurer earned $1.43 per share, compared with $1.90 a year earlier.

Analysts had expected an operating profit of $1.28 per share, according to Thomson Reuters I/B/E/S.

Net premiums written in North America fell 6.5 percent to $1.52 billion, primarily due to increased crop insurance premium payments to the U.S. government as a result of the government's crop insurance profit and loss calculation formula, ACE said.

U.S. crop insurance payments on losses caused mainly due to the drought last year have crossed $12.3 billion so far. Some experts say indemnities could top $20 billion, nearly double the old record set in 2011.

The company's property & casualty combined ratio, the percentage of premium revenue an insurer has to pay out in claims, rose to 105.5 percent from 93 percent.

Shares of ACE, which has a market value of about $29 billion, traded at life-highs earlier this month, and were up 15 percent in the six months to Tuesday's close.

The Thomson Reuters United States Property & Casualty Insurance Index has also gained about 15 percent in the same period.