WASHINGTON — AFTER years of hesitation, the West has finally unleashed the full force of its military air power in the Balkans. The question now is whether the munitions from massive NATO strikes will cow the Bosnian Serbs into real concessions at the peace table - or drag the West into a widening conflict it has long sought to avoid. NATO's airstrikes were launched Wednesday in response to earlier Serb shelling of Sarajevo. If this hard-nosed strategy works, the world may ask why it wasn't tried sooner. Success could have important implications for the amount of muscle employed in future United Nations peacekeeping operations. Failure could mean the withdrawal of the UN mission - something that would involve tens of thousands of US troops and could lead to a humanitarian disaster. ''It's a high-risk strategy,'' said UN spokesman Chris Gunness in Zagreb, Croatia. ''It could yet backfire.'' Limited NATO airstrikes against the Bosnian Serbs in May ended in humiliation, with the seizure of hundreds of peacekeepers as hostage insurance against further action. That's unlikely to happen this time, as most UN troops have been removed from vulnerable positions. Western NATO allies also appear firmly united in support of the use of punitive air power. In the past, Britain and France have expressed misgivings about military escalation in the Balkans. ''If the Bosnian Serbs continue to launch challenges, well, we will continue and even enhance our military activities,'' threatened NATO Secretary-General Willy Claes yesterday. Initial indications were that the airstrikes, launched in retaliation for the shelling of the Sarajevo market earlier this week, were a success. One target, a large Bosnian Serb ammunition depot outside of Sarajevo, appeared to have been heavily damaged, according to reports from Washington. Air-defense systems all across Bosnian Serb-held territory appeared to have been knocked out, leaving troops vulnerable to further NATO action. Worldwide reaction to the strikes was generally positive. Russia, however, a longtime Serb ally, expressed misgivings. Russian President Boris Yeltsin ''condemns any act of violence on the territory of the former Yugoslavia,'' said his press secretary Sergei Medvedev. United States aircraft made up the bulk of the strike force, which as of this writing had carried out four waves of attacks. ''The strikes right now are intended to try to indicate that we have the capability to do a significant amount of damage to military targets of the Bosnian Serb army,'' said US Adm. Leighton Smith, the NATO commander in charge of the air campaign. The bombing was also intended to make NATO seem more than a paper tiger. Bosnian Serb forces have long been safe in ignoring the West's threats. In recent months, for instance, Serb artillery has gradually moved back into the NATO-declared heavy-weapon exclusion zone around Sarajevo, once again making the battered Balkans capital a place of danger in the streets. Bombing ''should reinforce our credibility and convince [Bosnian Serbs] that peace through negotiations is a better option,'' says one US official in Washington. The Bosnian Serbs may already have been predisposed to settle differences at the bargaining table. On Tuesday, with the the threat of airstrikes already hanging heavy in the air, Bosnian Serb leader Radovan Karadzic offered to take place in US sponsored peace talks, and observe a cease fire while those talks occurred. Bosnian Serb reluctance to participate has long been cited by US officials as the biggest obstacle to a peace agreement in the former Yugoslavia. But Karadzic's offer, made in a letter to former US President Jimmy Carter, wasn't enough to persuade NATO leaders to stay their bombers' flights. FOR one thing, the Bosnian Serbs made no mention of whether they would drop their long-held demand to become a separate nation. They didn't say if they would be willing to surrender any of the territory they now control, which amounts to about 70 percent of the Bosnian nation. Though details of the latest US peace plan for the area haven't been made public, it's believed to call for almost an even split of Bosnian territory, with Bosnian Serbs to receive 49 percent and the Bosnian Muslim-dominated government to receive 51 percent. On Tuesday, State Department spokesman Nicholas Burns judged that Karadzic's letter to Carter ''contains some potentially positive elements.'' US officials now hope that Karadzic, facing up to NATO might for the first time, will be willing to be more specific in his offer. But willingness on the part of Karadzic may not be enough. NATO's strikes could exacerbate splits in the Bosnian Serb leadership, with hardliners such as military leader Ratko Mladic pushing stubbornly for continued fighting, at all costs.