WHEN Derek Hirst moved from city to country - from London to Sussex - in 1977, he didn't want to be a "landscape painter" as such. He didn't want to "confront it head on." He came to Sussex primarily to recover his health: "Place has always been very important to me." The move to a new, and rather overwhelming, nonurban place also meant "a personal change in attitudes."What Hirst came to see was that "landscape as metaphor" was what he wanted his paintings to be concerned with. The imagery of his paintings, though perfectly readable as landscape, is also abstract. He enjoys the freedom to move between the two. "They represent sea, sky, clouds, if you want them to." But they are also form, shape, color, and contrast of weight and substance, all contained in the paint and mixed media out of which they are made and in the way they are placed within the painting's rectangl e. He was always interested in Japan and its art, and a visit to that country in 1985 at last helped him "get his act together." On his last morning in Tokyo, Hirst thought he would have to leave without seeing Mt. Fuji. But there, incredibly, exactly framed by his 12th-floor window, was the mountain. This unforgettable "vision" prompted a series of paintings, "Sacred Mountain - Six Views." The "mountain" in these works is, very minimally, a triangle. The triangle is both abstract shape and factual mountain. It is like "the Japanese notion of theater," he says, when a chair might be placed on stage, and the actors react to it as a mountain - and then "it becomes one." The temple gardens in Kyoto, with their raked sand, moss, rocks, dry waterfalls, and cones of sand, intensified his conviction of landscape-as-metaphor: The small cones are mountains, the raked sand is the sea, and "the moss growing into the sand is like the interaction of the water and the land." Since the sea had become such an obsessive thing for his painting at home in Sussex, his memory of Kyoto's raked sand inspired a way to paint the sea without direct confrontation. In his painting "Golden Pond," the rippled, wavy lines in the lower area or foreground are in fact a candlewick bedspread glued to the surface and painted over. In "Three Kinds of Weather," he also brings to the lower regions of the image deliberate, tangible physicality - rope, sand, and plaster. "As you travel up the painting, it gets more and more illusionistic." And ethereal, perhaps. Another painting has actual gravel at its foot. It's as though you, the viewer, are standing on the beach, and ahead of you, and above, is the intangible expanse of ocean and air. The upper reaches of his large paintings have achieved this ethereal character as a development from works he has made using handmade paper and dyes, in which the substance of the paper actually began to disintegrate because of repeated soakings in dye. Thus the "weathering" of the painting process acts out the weathering of t he elements. And a fresh relationship between painted image and optical "reality" emerges: The painting doesn't "represent" or even "symbolize" the landscape. It acts it out in its own terms.