The White House said $214 million of Yugloslav assets in the United States had been blocked by presidential order. The amount includes $170 million at Yugoslav-owned banks.
President Bush, complying quickly with the United Nations sanctions approved on Saturday, signed the order hours later as he flew from California to Texas.
Banking sources said, however, that nearly $1.5 billion of Serbian-controlled assets had been moved out of Western banks in the past few weeks.
Sources said funds were transferred to secret accounts in Europe and may be difficult to trace.
The United States had already taken some trade and economic measures against Yugoslavia, which is now made up of the republics of Serbia and Montenegro.
The lastest U.S. action followed a fierce bombardment of Bosnia's capital, Sarajevo, on Friday as Serb-led forces attempted to seize territory in Croatia and Bosnia- Herzegovina.
Goal Is Explained
"It's our hope that this will help stop the senseless violence and help bring peace and stability to the region," said Judy Smith, a White House spokeswoman.
Mr. Bush said in a letter to congressional leaders informing them of his order that the measures he was taking "express our outrage at the actions of the Serbian and Montenegran governments and will prevent those governments from drawing on monies and properties within U.S. control.
"The grave events in Serbia and Montenegro constitute an unusual and extraordinary threat to the national security, foreign policy, and economy of the United States," he said.