The most apparent fact about Korean cookbooks in the United States is their scarcity. In Los Angeles, the proliferation of markets in Koreatown has made Korean ingredients far easier to find than information on what to do with them. The cookbooks occasionally found in Asian bookstores here are published overseas, not in the United States. That makes Koh's book worth noting, even though it is necessary to write the publisher to obtain a copy. One would expect such a book to come out of California or New York, but this one comes from Minneapolis. Its subtitle, "High-Fiber, Low-Fat Recipes," shows the author's emphasis on healthful cooking. The recipes are simply and clearly written, easy to follow even by those unacquainted with Korean food. To order the book, send $12.50 plus $1.50 postage to East-West Press, P.O. Box 4204, Minneapolis, Minn. 55414.