The Federal Reserve system sold a mammoth $6.9 billion in foreign currancies to prop up the value of the dollar in the weeks immediately following President Carter's Nov. 1 announcement that the United States would defend the value of its beleaguered currency.

Federal Reserve officials said the Central Bank used record amounts of West German marks, Swiss frances and Japanese yen to stop what they described and a "run on the dollar" that threatened "to undermine U.S. anti-inflation policies."

All together, the world's Central Banks "intervened" to the tune of $33.1 billion between Nov. 1 and Jan. 31 to prop up the value of the dollar to convince foreign currency traders -- banks, corporations and speculators -- that governments would no longer tolerate the rapid, disruptive decline in the U.S. currency.

The $6.9 billion intervention by the Fed dwarfed the previous three month record of $2.5 billion the Central Bank spent to defend the dollar between Aug. 1, 1978 and Oct. 31, 1978.

By January, Fed officials said the market had been convinced that the dollar would not continue to decline and sonce then the dollar has stabilized and risen somewhat.

As a result, the Federal Reserve was able to repay some of the marks, yen and francs it had borrowed from Germany, Japan and Switzerland. During the three month period from Nov. 1 to Jan. 31, the nation's net foreign currency sales totaled $4.9 billion.

When Centeal Banks, such as the Federal Reserve, intervene in currency markets they do so to keep the value of one currency from rising or falling too fast.

When the dollar is declining in terms of, say marks, the Fed can enter the foreign currency market in New York and offer to buy dollars in exchange for the West German currency. That action, usually carried out secretly through foreign currency dealers, increases the demand for the dollar and should keep it from falling.

But despite sizable intervention -- nearly $1 billion in the last four days of October alone -- the dollar continued to fall sharply, according to Scott Pardee, a senior vice-president of the New York Federal Reserve Bank. The New York Fed carries out all the open market transactions -- domestic and foreign -- for the Fed system and the U.S. Treasury.

On Nov. 1, President Carter announced a massive rescue operaiton for the dollar, saying that the value of the U.S. currency had declined much more than could be justified.

On Nov. 1, only a week after he unveiled his voluntary wage price guidelines to fight inflation, the President ontlined a series of steps the government would take to fight the decline of the dollar and convince buyers and sellers of currencies that the United States meant business.

He announced that the Federal Reserve would tighten monetary policy as a further step in the anti-inflation fight at home. That day, the Fed boosted the discount rate it charges banks that borrow from it to a record 9.5 percent from 8.5 percent.

The president also announced that the government has made arrangements with Germany, Switzerland and Japan to add up to $30 billion to U.S. holdings of foreign currencies that could be used to intervene in foreign exchange markets.

During the next few weeks the U.S. sold $5.9 billion of marks, $700 million of francs and $200 million of yen not only to keep the value of the dollar from falling further but at some points to creare enough demand for dollars to raise its value.