Gold coin dealers said that the price of South African krugerrands dropped yesterday as American buyers reacted to the possibility that importation of the gold coins to the United States may soon be banned.

Alan Posnick, vice president of Manfra, Todrella and Brookes, New York City coin and precious metal brokers, said the krugerrand has lost popularity to the royal maple, the Canadian gold coin, because buyers fear or incorrectly believe it will soon be illegal to own or trade krugerrands.

Under the proposed legislation, a final version of which passed the House yesterday but is pending in the Senate, the United States would provide an alternative to the krugerrand with an American gold coin. If the legislation is approved by the Congress and is not vetoed by the president, the coins will become available in the same sizes as the krugerrand -- four weights ranging from one-tenth of an ounce to a full ounce -- in October 1986.

The premium on the kruggerand has dropped from a high of 3 percent of the value of the gold content down to 1 percent, according to Posnick. The premium, a fee that is charged above the actual price of the gold in the coin, is linked to the popularity of the coin because buyers are willing to spend more on one that is widely accepted and easily traded.

According to coin dealers, that popularity is fading as fear grows that the market will become restricted or even illegal, despite reassurances by coin and gold dealers to the contrary. Bernard P. Zeng, manager and vice president of the Washington branch of precious metal and foreign currency dealer Deak-Perera, said that the price of the krugerrand slipped $4 yesterday to $338 because of the legislation, while the royal maple now goes for $342.

Experts said that the gold market would not be effected by the krugerrand import ban, since South Africa will be able to sell the same gold in the popular 400-ounce bars. According to one gold market specialist, South Africa only turns about five percent of its total gold output into krugerrands and can easily switch the production to the internationally traded bars if demand for the krugerrands fades.

The maple leaf's sales have recently outstripped those of the South Africa coin at both the Washington branch of Deak-Perera and at Manfra, Tordella and Brookes.

Ian M. T. McAvity, president of Deliberations Research Inc. in Toronto, is skeptical that a U.S. ban on imports would affect the South Africa economy. "It's hard to identify how much is politics and how much is marketing," he said, noting that Canada has made a stronger marketing effort on the part of the maple leaf in the last year.

South Africa produced 2.64 million ounces in krugerrands last year, and 685,000 ounces in krugerrands for the first 5 months of this year, according to McAvity. Canada produced just over a million ounces in the maple leaf last year.

In 1983, about $450 million of krugerrands were sold in the United States.

South Africa produced about 48.4 percent of the total world output of gold in 1983, the last year for which figures are available, according to Gold Institute statistics