The transformation of the United States from the world's largest creditor nation to its leading debtor -- with an estimated $400 billion owed to foreigners -- is no "cause for alarm," the Council of Economic Advisers said yesterday.

"This is not a dire threat to our future," council chairman Beryl W. Sprinkel told reporters.

The council's annual report also noted that the period of recent large trade deficits -- usually considered an unfavorable factor -- coincided with six years of prosperity in the United States, which in that period created many more jobs than Japan and West Germany, both of which often are praised for running trade surpluses.

"The deterioration of the U.S. external position began in earnest in late 1982, which also marks the beginning of the longest peacetime expansion in U.S. history," the report said. "The United States created 10 million new jobs between 1982 and 1986 -- almost five times as many jobs as Japan, and more than 100 times as many jobs as West Germany."

Critics of administration economic policy have said that the persistence of merchandise trade and current account deficits will boost the foreign debt to the point where it may cause a free-fall of the dollar, precipitate a decline in the U.S. standard of living, or both.

The Council of Economic Advisers' report said that persistence of current account deficits since 1982 resulted in a shift from a creditor position of $171 billion (in 1986 dollars) in 1981 to a debtor position of $264 billion in 1986.

Nonetheless, in a chapter in the economic report that takes a generally optimistic view on prospects for reducing both the trade deficit and the current account deficit, the council said the $400 billion total is less than 10 percent of gross national product.

"Assuming a 5 percent real rate of return, the income required to service these claims would amount to less than one-half of 1 percent of U.S. GNP," the report said.

The report acknowledged that persistent growth of the external debt (in assets) at last year's level -- 3.5 percent of GNP -- "would be a source of worry." At that pace, the net foreign claims by the end of the century would reach $2 trillion (in 1987 dollars), equal to 40 percent of GNP, and consume a full 2 percent of GNP to service the debt.

"This could present difficulties for the world financial system, especially if for some reason, foreigners suddenly become less willing to hold claims on the United States. Evidence of a steady reduction of the U.S. external deficit over the next few years will prevent these difficulties from emerging," the report said.

The report also points with satisfaction to the fact that the real trade deficit has been narrowing since late 1986, and predicts that further progress will be made. In a briefing, Sprinkel also revealed that by the end of next year the Commerce Department plans to make available monthly reports on trade volumes to go along with the monthly trade balances in dollar terms.

The latter reports, which showed growing deficits for most of 1987 despite the drop in the dollar, frequently stirred violent stock market reactions, even though the trend -- in volume terms -- at times appeared to go the other way. The administration hopes that the availability of improved data will put the trade picture in better perspective.

The CEA's report also said growth of the trade deficit in 1987 did not cripple the manufacturing sector, as some advocates of protectionist legislation allege. Nor, it said, do the trade imbalances result from unfair foreign practices, but primarily from "macroeconomic causes and require primarily macroeconomic solutions," the report said.