The U.S. dollar soared and gold plunged yesterday, as the Carter administration told international foreign exchange markets what they have been waiting for months to hear: The U.S. is searching for appropriate action to halt the dollar's slide. The reaction was loud and clear.

Gold tumbled from its record-high perch as the dollar rose. Gold's price fell $6.50 an ounce in London to $208.375, in Zurich to $208.125.

Trading was "extremely active" in Japan and Europe, but it slackened in New York as dealers awaited President Carter's news conference.

In Frankfurt, the dollar jumped almost 6 pfennigs to close at 1.992 marks, up from 1.9375 Wednesday.

In Zurich, the dollar closed at 1.6520 Swiss francs, its best value in a week, compared with 1.59785.

In Tokyo, where the dollar has lost a third of its value in a year, the dollar rebounded to 185.455 yen from 183.75 yen 24 hours earlier.

In Paris, where the franc has strengthened dramatically this week, dealers boosted the dollar to 4.335 francs from 4.2175 Wednesday.

In London, the dollar climbed steadily throughout the day, closing at $1.94 to the pound compared with Wednesday's 1.9760, a dollar gain of 3.6 cents during the day.