When the United States sent a special package of money to stimulate the Polish economy in the aftermath of Communism, everyone in Washington thought that it was a nice gesture to brave people. Like most foreign aid, the money was something that they thought they would never see again.

But now Washington is faced with a startling new species that it does not know how to handle, a successful aid program that can pay back its money to the U.S. Treasury.It should be simple. Instead, as the debate on NATO expansion resumes on Monday in the Senate, the Clinton administration and champions of Poland are having a testy fight about what to do with the proceeds of the sale of the $240 million in investments made here by the Polish American Enterprise Fund.

Last week the national security adviser, Samuel Berger, and one of his predecessors, Zbigniew Brzezinski, squared off in a meeting, with Brzezinski insisting that all the proceeds should stay in Poland.

Brzezinski, who was born in Poland and portrays himself as the country's No. 1 defender in Washington, said in an interview that a plan by the U.S. Treasury and the Agency for International Development to return half the fund's money to Washington would rob Poland of money that had been given as a grant. He accused the administration of making "a bureaucratic grab" of $120 million that would become lost in the Treasury bucket.

What to do about a particular foreign aid program in one country does not often engender much emotion, certainly not over a comparatively small amount of money. And such matters rarely involve the national security adviser. But the fund has been an odd breed that mixed private expertise and public capital. And because it has worked in stimulating business in Poland, where the economy is roaring at 6 percent annual growth, administration officials would like to showcase it as a model for the future.