CHINA FOR THE WEST: Chinese Porcelain and other Decorative Arts for Export, Illustrated from the Mottahedeh Collection, by David Howard & John Ayers (Sotheby Parke Bernet, two volumes, $170). Probably the most scholarly and beautiful books on the decorative arts to be published this year is China for the West. And well they should be -- with a price which approaches that of one of the small objets d'art under discussion. The useful introduction covers the history of China's trade with the West, pointing out, to the surprise of some, that the trade existed in Greek and Roman times. The heyday of the porcelain traffic was from the end of the 17th-century through 1830, and the authors estimate that more than 4000 china services were produced for the English market alone in the years between 1700 and 1820. Those who saw the "Splendor of Dresden" show at the National Gallery of Art and elsewhere, appreciate the tremendous impact on Europeans of the china. The China trade came later to the young United States, flourishing from 1784 and bringing to this country wonderful wares bearing the coats of arms and other devices of the new patriots. The book has 103 color plates and 700 monochrome illustrations, primarily of objects collected by Rafi and Mildred Mottahedeh of New York. The large 330 X 240 millimeter size is especially helpful to those trying to identify a piece from their own collection.