The Bank of Japan's quarterly "tankan" business sentiment survey is expected to show a decline in confidence among major manufacturers for the first time in 21 months, according to a recent poll of economists.

The findings of the closely watched survey, due out Wednesday, will reflect concerns about a possible economic slowdown in the United States resulting from higher crude oil prices and a drop in exports from Japan to China against the backdrop of Beijing's policy of curbing investments.

According to the Kyodo News poll of 23 private-sector economists, the central bank's index to gauge business sentiment among major manufacturers is expected to come to 22 on average, down four points from the September survey.

The index, which reflects overall economic activity, represents the percentage of companies reporting favorable business conditions minus the percentage of those reporting unfavorable conditions. A positive reading means optimists outnumber pessimists.

The yen's appreciation against the dollar is among other factors prompting the economists to predict a drop in the index.

The poll also found that the index measuring sentiment among major nonmanufacturers is forecast to drop by 1 point from the previous survey to 10.