WASHINGTON -- The Bush administration committed itself yesterday to joining in the use of military force if relief supplies are blocked by fighting in Bosnia-Herzegovina.
Raising the political risks for President Bush, the United States declared for the first time that it would "do its part" if force is required to ensure delivery of humanitarian aid to 300,000 Bosnians under siege by Serbian militias.
Administration officials did not spell out what it meant for the United States to "do its part."
The new U.S. position was announced as the United Nations Security Council, moving quickly to take advantage of a Serbian withdrawal from Sarajevo's airport, ordered 1,100 Canadian peacekeepers in to secure the field in preparation for the desperately needed flights of food and medicine.
As an early contingent of 200 peacekeepers raised the U.N. flag over the tarmac, France, which has assumed a high-profile role, announced that a French airlift containing 6 tons of medicine and other supplies had landed even before the airport was fully secured.
If all goes well, large amounts of aid could start moving in a few days, diplomats said, easing the danger of widespread starvation.
A U.S. role in airlifting these supplies was anticipated.
But the Security Council, mindful of the area's recent history of short-lived cease-fires and broken commitments, warned that in the absence of cooperation on the ground, it did not "exclude other measures to deliver humanitarian assistance to Sarajevo and its environs."
Delivery of relief has been blocked for weeks by heavy shelling near the airport by Serbian irregulars intent on crushing Bosnia's separation from what was Yugoslavia.
At the State Department, spokeswoman Margaret D. Tutwiler prepared the ground for another Security Council resolution aimed at protecting the relief mission:
"If the United Nations votes on a resolution to take all necessary measures to facilitate provision of humanitarian assistance to the people of Bosnia-Herzegovina, it would be an action that we would support, and as the president said last night, the United States will do its part."
"All necessary measures" is the standard language, used before the Persian Gulf war, by which the Security Council threatens military force.
An official who briefed reporters on Mr. Bush's trip next week to the summit of industrialized democracies said the United States hopes the threat of force is enough to persuade the Serbs to back off.
"That's our hope but it's not our assumption," he said. "Our assumption is that force will be required, and we're prepared to join others in making such a commitment . . . knowing what a difficult military environment this is. No one is under any illusions about that.
"The operational details have yet to be worked out," he said. "But we are prepared to make a commitment as part of a multilateral effort to provide military support to ensure safe passage of humanitarian relief convoys and or flights into Sarajevo."
The toughened U.S. stance reflects a new international determination -- advanced by the European Community on Saturday and dramatized by French President Francois Mitterrand's visit to Bosnia on Sunday -- not to allow the threat of armed interference to block the relief effort.
It moved the United States and European countries a major step closer to a dangerous and extremely complex international military mission that the Pentagon, fearing a quagmire, has been reluctant to contemplate.
The Joint Chiefs of Staff solicited the views of its commanders in Europe on possible courses of action to support a U.N. request for humanitarian relief two weeks ago, a Pentagon spokesman said.
The spokesman said he was unable to offer any specifics either on relief flights or contingency plans. The United States has pre-positioned relief supplies at Rotterdam in the Netherlands and at Pisa, Italy.
But other officials said plans for possible military action to ensure the success of relief efforts were now seriously under way.
One U.S. official said that to secure delivery of humanitarian aid would require controlling the ground around the airport, eliminating mortar, artillery and anti-aircraft fire and placing more troops along a land corridor.
Air cover may also be needed, the official said.
One Western diplomat acknowledged that any allied military involvement might eventually raise the question of moving beyond delivery of humanitarian aid to quelling the conflict that caused the nightmare in the first place.
Miss Tutwiler refused to be drawn into such speculation, saying actions contemplated are strictly humanitarian.