THE HAGUE, Netherlands -- Vowing to stay in Bosnia, NATO military chiefs Monday urgently reviewed ways of strengthening the UN's battered mission and avoiding a humiliating withdrawal of peacekeeping troops.


"There was great resolve and feeling of unity among the participating chiefs of defense staff, and general agreement on the ways in which the effectiveness of UNPROFOR could be improved," Dutch Chief of Defense Staff General Henk van den Breemen told reporters, referring to the UN Protection Force.


The meeting came as former U.S. president Jimmy Carter announced in Pale that Serb leader Radovan Karadzic had offered a four-month ceasefire in Bosnia. The two men held a daylong meeting in the Serb stronghold of Pale on Monday, and Carter was due to brief Bosnian leaders in Sarajevo on the offer late Tuesday.


Speaking at the end of the first day of a two-day meeting in the Dutch city of The Hague, van den Breemen declined to give any details of what was discussed by NATO nations with troops in the Bosnian mission and the U.S., Germany, Italy and the UN.


"First of all, and most important, all of the chiefs of defense staff declared their determination to continue UNPROFOR's mission," van den Breemen read from a prepared statement.


The military chiefs are looking at proposals, pushed by France and the United States, for more equipment, redeploying small groups of peacekeepers into larger units, and the opening of an aid corridor from the Adriatic to Sarajevo.


NATO defense ministers summoned the chiefs of staff last week after endorsing contingency plans to pull out the peacekeepers in the event of a final collapse of the mission, now facing near daily humiliations.


Hundreds of the 23,000-strong UN force in Bosnia have been held hostage by Serbs as human shields against possible NATO air strikes in retaliation for violations of UN "safe havens" and attacks on peacekeepers.


Van den Breemen said the talks focused on ways to improve UNPROFOR's effectiveness within the existing UN mandate, and said any suggestions would be passed on to national capitals and the United Nations for final decision.


"The purpose of the meeting is to develop specific steps which could be taken to strengthen UNPROFOR's effectiveness in Bosnia-Herzegovina," he said, "and to determine the resources required to implement strengthening initiatives."


NATO diplomatic sources said the meeting could be one of the last chances of saving the mission and avoiding a withdrawal, which would have disastrous consequences for the UN's reputation and peacekeeping operations worldwide.


"Our soldiers on the ground are in a stalemate situation," Dutch military spokesman Navy Captain Frits Olivier told reporters. "Sometimes they are denied freedom of movement. That is unacceptable of course."


The chiefs of staff were joined Monday by Russia's envoy in Brussels, the seat of the North Atlantic Treaty Organization, Vitaly Churkin.


Churkin declined to disclose any details of the military options before the chiefs of staff, but said there were some new ideas on the table.


"We had a good brainstorming session. Yes, there were some new ideas," he said after the first day of talks.


Moscow, a key member of the five-nation "contact group" trying to broker a peace plan for Bosnia, has so far resisted tough action against the Serbs, often creating tensions with other group members: the U.S., Germany, France and Britain.