More Americans are investing in art, antiques, jewelry, rare books and stamps, for security rather than speculation.Judging by the recent record sales at Sctheby Parke Bernet, the nation's leading auction house.

Since September, Parke Bernet has experienced a 53 per cent increase in its net turnover in North American over the same period last year. During the first half of the auction season, the total net sales was $43,880,000.

John L. Marion, president of Parke Bernet, said, "Our sales this year have been characterized by generally high prices, greatly increased consignments, and by buyers' and sellers' confidence in our way of handling auctions."

Generally, said the auction firm, every field of collecting has participated in the generally robust market. "Now the Americans are the big buyers. In the early 1970s it was the Japanese," said Martin Stansfeld, a representative of the firm, "before the Americans had the idea of speculating in art. But that approach has been knocked down and replaced by a European notion - the Europeans keep a portion of their investments in tangivles for security."

So far, sales have been particularly good in American bronzes, coins, 19th-century European paintings, modern first editions, American paintinfs, scientific books, manuscripts, and jewelry, which alone brought a net total of $7,136,070 in New York.