The U.S. economy will no longer get $10 billion a month in investments from Japan, Germany and other nations because they now need the money at home, specialists say.

But the money will be less needed here because the federal budget deficit is going down and fewer U.S. bonds will need to be sold to foreigners, the specialists said Monday at a meeting of the Institute for International Economics, a private study group.Americans are earning more foreign money by selling goods abroad because the dollar has declined in value and made the U.S. goods attractive for foreigners to buy.

Some of the foreign money has gone into such projects as the Japanese purchase of Rockefeller Center in New York and made for bad feeling between the two countries. The Japanese had to buy the dollars needed for that purchase and many others by selling yen.

Americans needed the yen to pay for goods they bought in Japan. As Americans sell more goods, they will have more yen at their disposal.

The need for foreign funds could rise if war starts in the Persian Gulf at a cost estimated as high as $30 billion a month, said Rudolph G. Penner, a former director of the Congressional Budget Office.

Otherwise, Penner saw the current slowdown in business as a short one, although the recovery sluggish if major companies have trouble finding the new capital they will need.

Robert D. Hormats, a former assistant secretary of state, said Japan and Germany will be using more of their money at home. Japanese banks are having problems because the prices of stocks and real estate have gone down, he explained. Japan is also under international pressure to spend less abroad and more on increasing its own people's living standards.

"The estimated cost of German unification has now gone up to 140 billion marks (about $95 billion)," Hor-mats said. "Probably it'll go up again."

He agreed with Penner that war in the gulf would bring economic and well as human and political problems. "War has a voracious appetite for capital," said Hormats, who is vice chairman of Goldman Sachs International, a leading investment bank.

William R. Cline, a senior fellow at the economics institute, said the U.S. need for foreign money has declined because the drop in the value of the dollar has made U.S. exports more attractive and brought in more cash. Slower growth for the United States as a whole slows down imports and the outflow of money to pay for them, he noted.