* Macquarie analyst sees $3.05/lb resistance in arabicas
* Cocoa prices hold up despite Ivorian export outlook
* Thai sugar likely delivered against Friday's ICE expiry
* COMING UP: Liffe softs markets closed Friday, Monday (Adds byline, dateline, was LONDON. Updates prices, adds analyst comment, price table)
By Marcy Nicholson and David Brough
NEW YORK/LONDON, April 28 (Reuters) - ICE arabica coffee futures shot up above $3 per lb to a 34-year high in thin dealings on Thursday, bolstered by investor buying as the dollar sank to a three-year low.
Raw sugar sank to a 6-1/2-month low, pressured by ample supplies from Brazil and Thailand, while cocoa surged in heavy volume as options-related dealings forced shorts to scramble for cover.
Liffe's London-based commodity markets are shut on Friday and Monday due to U.K. public holidays, reopening on Tuesday.
The dollar index, a measure of the greenback's strength against a basket of major currencies, fell to a 3-year low after the U.S. Federal Reserve signaled it will not reverse low interest rates to support economic recovery.
The key July arabica coffee futures surged to a new high of $3.0340 per lb, buoyed by the weak dollar, tight supplies of high-quality beans and strong charts.
"The weaker dollar -- if it is sustainable -- will help matters from a speculator's viewpoint," said Kona Haque, soft commodity strategist at Macquarie Bank in London.
She noted a lack of origin selling and said that if dollar weakness persisted, the market had room to go higher with a key near-term resistance level of $3.05 per lb.
"I suspect the $3.05 level is as far as it's going to get before it starts falling," Haque said.
ICE July arabica coffee futures were well off their highs and up 2.35 cents to $2.9875 per lb at 1546 GMT. Liffe July robustas gained $18 at $2,554 a tonne at 1546 GMT, having earlier hit a contract high of $2,572.
Raw sugar futures on ICE tumbled, weighed by expectations of ample production of the sweetener from Brazil and Thailand and the possibility of further unrestricted exports by India.
India has approved around 30,000 tonnes of unrestricted sugar exports, kicking off overseas sales of a total 500,000 tonnes given an official green light on April 19, government sources said on Thursday.
Dealers focused on the expiry of the ICE May raw sugar futures contract on Friday and anticipated delivery of predominantly Thai raws after larger-than-expected output in the Asian country.
ICE May raw sugar futures fell 0.64 cent or 2.6 percent to 23.91 cents a lb at 1547 GMT. Open interest fell to 30,314 lots on April 27, the equivalent of 1.54 million tonnes of sugar and down roughly 20,000 lots from the previous day.
Key July dropped 0.54 cent to 22.42 cents per lb, hitting a 6-1/2-month low at 21.94.
"The sugar market's going down on momentum," the New York dealer said, adding demand was lower than expected.
London August white sugar fell $11.50 or 1.8 percent to $615 per tonne.
Cocoa futures surged for the second straight day, boosted by the softer dollar, with the focus on Ivory Coast as dealers awaited news about the mid crop and the resumption of exports.
On ICE, delta buying in options forced heavy short-covering on the futures market, dealers said.
"There are lots of options open at $3,300 and I think a very complacent trade, all short, found themselves scrambling," one veteran cocoa dealer said. "Also, I think there is some element of cocoa and coffee as safe havens from the volatility in sugar and cotton."
ICE second-month July cocoa futures surged $111 or 3.5 percent to $3,279 per tonne at 1548 GMT. Total volume jumped above 20,000 lots, the highest in two weeks with two more hours of trade still remaining.
Liffe July cocoa jumped 50 pounds or 2.6 percent to 1,977 pounds per tonne. * Prices as of 1552 GMT Product Last Change Pct Move End 2010 Ytd Pct ICE sugar 23.97 -0.58 -2.36 32.12 -25.37 ICE coffee 298.60 2.20 +0.74 241.80 23.49 ICE cocoa 3277.00 109.00 +3.44 3052.00 7.37 Liffe sugar 615.10 -11.40 -1.82 777.50 -20.89 Liffe coffee 2552.00 16.00 +0.63 2097.00 21.70 Liffe cocoa 1981.00 54.00 +2.80 2029.00 -2.37 CRB index 365.87 0.05 +0.01 332.80 9.94 Crude oil 112.70 -0.06 -0.05 91.38 23.33 Euro/dlr 1.48 0.03 +2.41 1.34 10.55 * ICE sugar and ICE coffee in cents per lb, ICE cocoa, Liffe sugar and Liffe coffee in dollars per tonne. Liffe cocoa in pounds per tonne. (Editing by Rene Pastor)