America's debt to the rest of the world jumped by 25 percent to $663.7 billion last year, according to new federal figures. But in releasing them yesterday, the Commerce Department omitted that bottom-line total -- which underscores the United States's position as the largest debtor nation -- saying the figures were not reliable.

Allan H. Young, director of the Commerce Department's Bureau of Economic Analysis, said the government withheld the total because current numbers understate the worth of U.S. overseas investment by valuing them at prices paid as long as 40 years ago. Foreign investments in the United States, by way of contrast, are more recent and their worth is considered closer to their actual value.

Young said government economists are studying ways to end the distortion and when they do, in the next year to 18 months, the department will begin publishing the bottom line on the U.S. international debt.

According to the figures released yesterday, direct investment in the United States -- investments which gave foreigners control of 10 percent or more of U.S. companies -- surged by $72 billion in 1989, to reach a total of $401 billion. Direct investment by U.S. companies in foreign countries grew $40 billion to a total of $373 billion.

The larger category of total investment, which includes such things as bank deposits and ownership of government securities, also showed the United States in debtor status: U.S. ownership of assets abroad totaled $1.412 trillion, compared with foreigners' holdings in this country of $2.076 trillion. The difference is the $663.7 billion figure.

Yesterday, congressional Democrats and private economists complained that the government was using the statistical arguments to hide one of the most embarrassing economic results of the Reagan and Bush presidencies: the conversion of the United States from the world's largest creditor nation as recently as 1983 to the largest debtor nation.

"The administration is trying to redefine our global debt problem instead of dealing with it," said Senate Finance Committee Chairman Lloyd Bentsen (D-Tex.). He said government concerns about accurate data "would be more understandable if these changes had been proposed seven years ago -- when the United States was the world's largest creditor nation."

In March, Council of Economic Advisers Chairman Michael J. Boskin told a congressional panel that current statistical collection was inadequate but would be improved, and administration officials yesterday denied there was any political motivation behind the decision to omit the bottom line. Marion C. Blakey, public affairs director for the Commerce Department, said the decision was made solely on economic grounds and is part of a government-wide effort to improve its statistics. Further, she said, "there's nothing that keeps anyone from finding it" by simply adding its component parts.

Economists agreed that the data is faulty. But C. Fred Bergsten, director of the Institute for International Economics, who is working on a book about the United States's debtor status, said his studies show that the bottom line is unlikely to change because U.S. overseas assets, such as debts owed by Third World nations, are also overstated.

Jeff Faux, head of the labor-backed Economic Policy Institute, agreed there is a statistical reason for improving the data, but added that omitting the total U.S. debtor position "suggests a sensitivity to the political embarrassment from the number."

Stephen Cooney, director of international investment for the National Association of Manufacturers, said, "the latest increase in America's foreign debt should certainly not be ignored, even if there are various interpretations of the actual totals."