An assault on Yugoslav President Slobodan Milosevic's authoritarian regime carries massive risks.
For one, the use of United States-led NATO forces - including some 400 jets - might lead to losses of allied pilots.
And expected Serbian retribution against Kosovo's ethnic Albanians could exacerbate already huge refugee flows in the Balkans.
Attacks on Serbia would also damage US relations with Russia, China, and other states opposed to NATO intervention.
Not acting, however, could also carry huge costs for the US and its allies.
More atrocities and refugees could lead to the war exploding into Albania and Macedonia, threatening the stability of the entire region and fueling doubts about NATO's post-cold-war purpose on the eve of its 50th anniversary.
Yet questions persist about NATO's objectives and potential for success in ending almost a year of fighting in Kosovo, an ethnic Albanian-dominated province of Serbia that Milosevic has ruled with an iron fist for a decade. An attack against a sovereign state would be a first in NATO's 50-year history.
"I don't think anybody knows the endgame," a Western diplomat conceded March 23 after the failure of a second round of 11th-hour talks between Milosevic and US special envoy Richard Holbrooke.
President Clinton says airstrikes would be aimed at "degrading" the ability of Serbian forces to press an onslaught against ethnic Albanian rebels and civilians. Some officials also hope airstrikes would compel Milosevic to accept the peace plan. The plan, which ethnic Albanian leaders signed last week, would give Kosovo self-rule from Serbia but deny it independence, and calls for a NATO peacekeeping mission.
"Whenever we can stop a humanitarian disaster at an acceptable price, we should do it," Mr. Clinton said at his news conference on March 19.
US officials assert that NATO bombing in 1995 helped push Milosevic into talks that ended almost four years of fighting in Bosnia, where he armed and financed Bosnian Serb secessionists.
Some experts also believe that Milosevic is secretly hoping for bombing because it would boost his popularity while providing him with the political cover to accept the peace plan and rid himself of the political and economic burden Kosovo represents for him. Indeed, it may be on this scenario that the Clinton administration calculations are riding.
In addition to the massive drain of Kosovo on Yugoslavia's already-devastated economy, there is little prospect that Serbian forces can fully eradicate ethnic Albanian rebels of the Kosovo Liberation Army (KLA). The 2 million ethnic Albanians have Europe's highest birthrate.
But some US officials and independent experts worry that Milosevic will refuse to bend even under the most withering NATO pounding. That could augur several scenarios, all of which would carry extremely high prices.
"If Milosevic feels he can make personal political gain ... he may try to ride out the first part of the firestorm," says a Pentagon source. "We are assuming that by destroying his military and police forces we could have a negative impact on him. But it could take us a long time to get to that."
Under one possible outcome, outcries over casualties and pressure from Russia, other countries and Congress could force Clinton to call off the raids. That would leave Kosovo's ethnic Albanians open to massive retribution and Milosevic's power more secure than ever before.
He might even be emboldened to move against his main opponent, Milo Djukanovic, the pro-West president of tiny Montenegro, which with Serbia is what remains of Yugoslavia. Mr. Djukanovic has for months rejected the legitimacy of Milosevic's regime and set Montenegro on a path that could lead to secession. An attempt by Milosevic to dislodge Djukanovic could trigger a civil war in Montenegro.
Another scenario: Milosevic may be calculating that by riding out airstrikes, he would be in a strong position to set the terms for a new peace accord that would meet his demands.
A third possibility is that the gradual destruction of the Yugoslav Army and police could send the KLA on the offensive and collapse two major pillars of Milosevic's rule, plunging Serbia into chaos that could spill into other parts of the region.
The regime's cohesion is thought to be weak, a view bolstered by Milosevic's purge in the midst of crisis on March 23 of Lt. Gen. Aleksandar Dimitrijevic as Army security chief. His ouster comes after a massive purge of the top ranks of the Army and federal police late last year.