UNITED NATIONS — Officials here are scrambling to rescue a proposed peacekeeping force designed to enforce a truce in Lebanon, after France stunned Turtle Bay by retreating from its role as leader and would-be “backbone” of the U.N.-led force.

As the Lebanese army yesterday began to deploy in areas in southern Lebanon that were gradually evacuated by Israel, 49 countries, considered candidates to contribute to the enhanced, more “robust” U.N. force, debated how to deploy troops meant to support Beirut. They also hashed out the rules of engagement that would guide their presence there.

The discussion was conducted under a cloud created by President Chirac’s announcement in Paris that at this stage his country was willing to commit no more than 200 troops to the proposed U.N. force.

Diplomats said that Paris defense officials were much more timid about contributing troops than their foreign policy counterparts. Defense Ministry officials said the mandate of the proposed force was unclear, although Security Council resolution 1701, which defined that mandate when it was unanimously adopted a week ago, was largely written by French diplomats.

Mr. Chirac had to consider all the conflicting interests raised by his aides, as well as the political situation in Lebanon, before making a decision, a French official speaking on condition of anonymity told The New York Sun.

A day after a quick visit to urge Secretary-General Annan to hasten the force’s deployment, the Israeli foreign minister, Tzipi Livni, was considering a similar trip to Paris, to urge Mr. Chirac to enhance the French contribution, another diplomat said.

“We were disappointed,” said the U.N. deputy secretary-general, Mark Malloch Brown, who presided over yesterday’s troop-donor meeting. “We had hoped France would do more.”

He nevertheless added that “it did not deter others from coming forward with offers” for supporting the force, which according to the council resolution should boost the current 2000-troop U.N. Interim Force in Lebanon to as many as 15,000 troops.

But when pressed to say whether it would be possible to meet a call he had made at the conference for deploying as many as 3,500 troops within 10 days, to secure an uneasy truce on the Israeli-Lebanese border, Mr. Malloch Brown could not cite any concrete commitments, and at best, he said that a third of the 23 countries that spoke yesterday made a “relatively firm commitment” to join the force.

Early yesterday President Chirac released a statement, saying that France at this stage would contribute only 200 engineers to support the 200 French troops already serving as part of UNIFIL, which has been in Lebanon as an interim force since 1978.

According to the statement, 1700 French troops on ships off the Lebanese coast remain ready to assist UNIFIL, although not necessarily under the U.N. flag, as required by the council resolution. It wasn’t clear when, or even if, those troops would go on Lebanese soil. No decision has yet been made, and it was not clear when Mr. Chirac would make it, the French official said.

Many potential troop contributors shied from commitment due to a growing sense that the task of disarming Hezbollah, a central demand of relevant Security Council resolutions, would be more foreboding than first envisioned. The unease intensified amid several belligerent statements made by Hezbollah leaders and their sponsors in Tehran and Damascus in recent days.

The confusion about the role of the force was not made easier by Mr. Malloch Brown, who tried to describe what he called “prudently designed rules of engagement.” The force, he said, would be “non-offensive in character,” but the rules would allow troops “to robustly use force, if it’s necessary.”

There would be “no large scale disarmament of Hezbollah,” he said, but rather “policing a political agreement.”

Italy was said by diplomats who participated in Thursday’s meeting to conditionally pledge troops for the early “rapid” deployment.

Bangladesh, Indonesia, Malaysia, Nepal, and Denmark also spoke of joining the force.

Britain pledged a frigate, reconnaissance planes, and helicopters, as well as an air base it controls in neighboring Cyprus.

Germany assumed a leadership role in one of the most crucial tasks: assuring Hezbollah would not rearm.

The German U.N. ambassador, Thomas Matussek, said once the parliament authorizes it, his country was ready to supply “a rather substantive maritime component” to enforce the arms embargo, as well as policing troops to patrol the border with Syria.

Mr. Matussek told the Sun that some in his country question the heavy burden on the military, as 8,000 German soldiers already serve in posts around the world. In addition, he said, there is Germany’s “history and the special responsibility for Israel.” It is therefore trying to “tailor our contribution in a way that the situation cannot arise where a German soldier would have to confront an Israeli soldier.”

Other diplomats said Israeli concerns about troops from countries that do not have relations with the Jewish state would not be taken into account.