Ample supplies of Cuban raw sugar to Japan, a major buyer, are keeping the sugar markets bearish and are likely to lead to heavy deliveries against Tokyo Sugar Exchange futures later this month.

The world's most actively traded sugar futures contract on the New York Coffee, Sugar & Cocoa Exchange excludes delivery of Cuban-grown sugar.Earlier this year, the consensus was that Cuba would have difficulty with harvesting the crop because of fuel shortages. But many analysts now say the markets have little to worry about.

Thai raw sugar sales, a major source of futures delivery world sugar, also are continuing apace, leaving Japanese buyers with few concerns about garnering stocks.

"I don't think there's any reason for them to be worried about supplies," said one Australian industry contact, saying that Japan's sugar needs appeared to be well-covered for the first half of 1992.

Tokyo's sugar futures market remains a key point for shipments, particularly from Cuba, to enter Japan's market. Cuban sugar is more attractive to deliver because trade house dealers said they can sell Thai sugar directly to refiners at a slight premium to Cuban.

"We have abundant sugar coming to Tokyo for delivery" against the May contract, said a Tokyo trade-house dealer. The May contract expires March 31, and its delivery period is April 15 to the end of May.

Up to 60,000 metric tons of raw Cuban sugar is likely to be delivered against the May contract if current world price relationships remain stable, dealers said. That would be about twice as much Cuban sugar as Japan imported in January, and about half of January's total raw imports, according to the most recent government data.

May sugar futures in Tokyo closed Wednesday at US19 cents (25.8 yen) a kilogram, up 0.5 yen as the U.S. dollar rallied against the yen. The key short position holder is said to have sold over the 26 yen level, making delivery profitable.

On top of the influx of Cuban sugar, Thai crushing continues with no sign of abatement as mills operate at close to the nation's capacity of 450,000 tons a day, a Bangkok trade source said.

Thai sellers now also have more incentive to sell raw sugar instead of refining to white because of the recent freight change on Thai white sugar delivered in London.

The bearish supply factors mean Thai sellers, who continue to seek higher premiums to sell raw, may not get them. The current Thai free-on-board May- June premium was quoted by traders mainly between 20-25 points over New York May futures, although some prompt cargoes may be commanding a higher price.

Asian trade sources indicated that they continue to meet resistance from Thai sellers.

"You ring the millers up, and they are reluctant to talk sensible prices," said a Southeast Asian sugar industry official.

But although Thai mills say they are waiting for a 35-point premium and appear to be unwilling to negotiate, some Asian dealers said certain mills will sell at current levels.

China also is disappointed with low sugar prices, particularly those for white sugar, Hong Kong trade sources said.