WASHINGTON -- Issuing a fresh threat to Bosnian Serbs, the White House warned Thursday that the United States may defy the international arms embargo in Bosnia despite objections from United States allies.


An increasing number of Congress members feel the embargo favors the Bosnian Serbs, who have been supplied by Yugoslavia's Serb-dominated government and enjoy an overwhelming superiority in heavy weapons.


The United States is trying to force an agreement between the Bosnian Serbs, the Moslem-led Bosnian government and the Croats.


Lifting the embargo without the support of U.S. allies "would be a last resort," Press Secretary Dee Dee Myers told reporters.


Myers called the announcement from Yugoslavia "a positive step." She said the U.S. will look for signs that Yugoslavia keeps its word. "We'll have to watch and see if that border actually seals up," she said.


For months, President Bill Clinton has sought to lift the embargo but said doing so without support from U.S. allies would undermine peace talks and the NATO alliance. France and other NATO allies with peacekeeping forces in Bosnia have said a unilateral move by the United States would expose the peacekeepers to attack.


However, House and Senate negotiators neared an agreement Wednesday on pushing the Clinton administration to defy the embargo on the former Yugoslavia.