The gulf war, which ended two months ago, is still casting a shadow over the international diamond market, the world's top producer said.

"At this stage the influence which the gulf war will have had on the world economy is still difficult to measure, and the outlook for 1991 remains unclear," De Beers Consolidated Mines Ltd. said in its annual report.However, chairman Julian Ogilvie Thompson added that the quick end to the war and signs of growing consumer confidence in the United States left room for optimism.

The company's London-based Central Selling Organization, which markets four-fifths of world rough diamond production, had sales of $4.17 billion in 1990, up a modest 2 percent from the previous year.

"In the early part of 1991 the rough diamond market was dominated by the war in the gulf, which curtailed polishing activity in Israel for several weeks and reduced trading activity everywhere," Ogilvie Thompson said.

Economic prospects remained uncertain, and the recent strengthening of the dollar could affect sales outside the United States.

He said more expensive diamond jewelry sold well in both the United States and Japan in 1990 despite the difficult climate. Cheaper stones, which are polished mainly in India, fared less well.

De Beers' Central Selling Organization would maintain its policy of adjusting supply of rough stones to cutting centers to keep prices stable, Ogilvie Thompson said. It would also continue steady buying from producers.