Gillette Co. said late yesterday that it will report weaker-than-expected results in the second quarter because of disappointing sales and continued weak markets overseas.

The company waited until the New York markets had closed before announcing its downbeat forecast. As the world's largest manufacturer of razors and blades, Gillette is one of the few companies whose sales and profits can move markets because investors believe their results provide an eye on the economy. In August 1997, the Dow Jones industrial average fell 247 points after Gillette and other consumer products companies, including Coca-Cola Co. and Procter & Gamble Co., warned of lower earnings.

Gillette said its second-quarter earnings will be about 20 percent lower than a year ago. Analysts surveyed by First Call Corp. had predicted a 12 percent decline, to 29 cents a share. The company earned 33 cents in the year-earlier period.

The company said its sales are expected to register what it called "a low single-digit increase." Analysts had anticipated an increase in sales of about 5 percent.

The company said sales in particular were disappointing for its Braun appliances, Paper Mate pens and toiletries products.

Companies such as Gillette -- which earns two-thirds of its revenue outside the United States -- and Coca-Cola are particularly sensitive to financial downturns in global markets. Gillette said yesterday that "slower-than-anticipated recovery in several key markets," including Brazil, Germany, Japan and Russia, contributed to weaker-than-expected results.

Gillette said it should return to "more traditional" rates of sales and profit growth by the end of 1999, helped by new products in the second half of the year.

On the positive side, the company said that three major new products -- the Mach3 shaving system, Duracell Ultra batteries and Oral-B Cross-Action toothbrush -- have been well received and are resulting in higher sales and market share.

Gillette's shares fell 43 3/4 cents, to $47.31 1/4, before the announcement in trading on the New York Stock Exchange.

Apparently acting to stabilize its stock price, Gillette also announced an expanded share-repurchase program. The company said it would buy back an additional 25 million shares over the next 12 to 18 months, after completing a repurchase of 50 million shares by the end of this year.