Japanese tourists shell out so much money for macadamia nuts when they visit Hawaii that Agriculture Department trade analysts refer to the nutty souvenirs as suitcase exports.

Macadamia nut production is also catching on in California, and in other countries. American output has more than doubled since the late 1970s to an estimated 5,900 metric tons in 1989.John O'Connell of the department's Foreign Agricultural Service said world macadamia production has been growing rapidly, including a 60 percent increase in Australia since 1987. A sharp expansion is also indicated over the next decade in Africa and Central America.

"With trees popping up all over, it has been estimated that the world supply of macadamia nuts will double in five years and triple in 10," Mr. O'Connell stated in a published report. That will cause producing countries to "compete fiercely for export markets," he said.

Mr. O'Connell added in a telephone interview that the so-called suitcase exports of macadamia nuts to Japan are almost impossible to estimate accurately, although $15 million annually may be conservative.

The value of direct nut exports is approximately $5 million a year, meaning that the suitcase shipments are at least triple the known level, he said.

In his report, Mr. O'Connell said the Japanese custom of giving gifts after returning from a vacation is behind the macadamia mania.

"Local retailers in Hawaii have observed that a Japanese tourist will often buy several boxes, or even a case of macadamia nut products, while mainland U.S. tourists usually buy only one or two boxes," he said.

Several other Asian markets are developing, including Hong Kong, Singapore and South Korea. But if promoters have their way, the biggest export prize yet may be Europe, where macadamia nuts are a relatively unknown oddity.

Mr. O'Connell said macadamia trees are native to Australia, but commercial nut production began in Hawaii after World War II. The nuts are similar in size and shape to filberts but have a taste and texture all their own.

Harvested nuts are de-hulled, cracked and roasted before being processed into salted, candy-coated or chocolate-coated forms, or used as ingredients in bakery, dairy and other products.