The price of gold plummeted on international bullion markets yesterday in what European dealers called a reaction to an easing of political tensions in Indochina and to the renewed flow of Iranian oil. The dollar improved.

Gold plunged $11.125 in Zurich to $237 an ounce from $248.125 Friday and recouped a bit in London but still was down $8 to $238.25 an ounce. In New York, gold's closing price was $236 an ounce.

European closing prices for the dollar, with the New York close in parentheses: Frankfurt, 1.86 marks, up from 1.8580 Friday (1.8587); Zurich, 1.6782 Swiss francs, up from 1.67645 (1.6775); Paris, 4.2890 French francs, up from 4.28 (4.2890); Brussells, 29.755 Belgian francs, up from 29.70 (29.39); Amsterdam, 2.0065 guilders, up from 2.0045 (2.006); Milan, 842,20 lire, up from 841.70 (842.10).

In London, the pound dropped to $2.0225 from $2.0270 ($2.0233).

In Tokyo, the dollar scored a substantial gain to close at 205.20 yen compared with 203.45 Friday. Market sources said the Bank of Japan intervened in early trading but withdrew in the face of aggressive buying.