May 5 - Gap Inc forecast first-quarter earnings below market estimates, as it wrestles with rising raw material costs and the impact of the March earthquake in Japan -- home to almost all the company's 150 or so Asian stores.

Gap Inc.'s new flagship store in the up-market Ginza shopping district in downtown Tokyo

Gap, which also operates the Banana Republic and Old Navy chains, expects to earn 38-39 cents a share in the first quarter. Analysts have predicted earnings of 40 cents a share.

The company, which warned of a significant drop in merchandise margins, also said its design head Patrick Robinson will leave the company.

Gap said its April same-store sales rose 8 percent, with all three of its brands posting positive numbers.

Most retailers enjoyed a significant boost last month from late Easter sales. For the quarter, Gap's same-store sales were negative at all its divisions.

Shares of the company were down 1 percent at $22.81 on Thursday before the bell. They closed at $23.13 on the New York Stock Exchange on Wednesday.

(Reporting by Nivedita Bhattacharjee, Editing by Ian Geoghegan)