JERUSALEM — Moves to deploy an international force in southern Lebanon gathered pace yesterday as America and Britain tried to find a formula that stands a credible chance of bringing a lasting cease-fire.

Plans are expected to solidify at a crisis conference in Rome on Wednesday when Secretary of State Rice will meet the foreign ministers of Britain, Russia, France, Italy, Lebanon, Saudi Arabia, Egypt, and Jordan.

“We and the U.S. are brainstorming a lot of ideas to find a formula that works,” a Foreign Office official said. “If we do get agreement, there is going to be some pretty quick footwork. We will not be held back by NATO or Brussels bureaucracy.”

However, diplomats and experts expressed doubts about the feasibility of any early deployment and said they thought that governments would not be in any rush to send troops into a highly complicated and dangerous situation.

The proposal for a multinational deployment received an unexpected fillip when Israel reversed its traditional policy and embraced the idea of foreign troops underwriting the security of its northern border.

“We support the deployment of a multinational force with broad authority,”Defense Minister Amir Peretz said. His remarks were echoed by Shimon Peres, the vice premier, who said he supported the idea of a “serious” outside intervention.

“It does not matter who runs the mission,” he said. “It is just important that the mission is accomplished and the Lebanese border is cleared of Hezbollah missile-launching pads.”

The task is to construct a force that has the confidence of all sides and the mandate and means to act decisively.

The E.U. foreign policy chief, Javier Solana, said several European countries were ready to contribute troops. France, which has strong historical and political links with Lebanon, was being spoken of as a possible candidate to lead a deployment, with Turkish backing. Mr. Solana said a force under the umbrella of the U.N. Security Council was “a real possibility.”

Nobody is underestimating the difficulties of the project. A French diplomat said, “There will have to be a real cease-fire before anything can happen.”

That will require both sides to claim victory without undue loss of face, a situation that seems remote at present.

Israel will need to have secured the return of two kidnapped soldiers and an end to Hezbollah rocket attacks. Hezbollah will have to reach a point where material and physical losses outweigh the kudos it has won in the region through its defiance of Israel.

Western diplomats said any deployment would be meaningless unless it had the power to enforce U.N. resolution 1559. That calls for the extension of the Lebanese army’s mandate to the Israeli border and the disarming of Hezbollah.

If Hezbollah handed over its rockets and guns, it would abandon its raison d’etre of destabilizing Israel and renounce the activity that gives it its credibility and traction in the Arab and Muslim world.

Analysts were also questioning where the troops would come from. Mr. Peretz’s preference is for a NATO force, but its involvement would be politically and organizationally difficult.

NATO is seen in the region as representing American, and by extension Israeli, interests. It is also severely stretched by its commitments in Afghanistan, where it has nearly 15,000 troops, as well as the Balkans, Africa, and Iraq, and would be hard-pressed to find the 7,000 troops that it regards as the minimum requirement for Lebanon.

Any force is more likely to operate under a U.N. or E.U. flag. Germany said it would consider any request for troops as part of a U.N. force but only on condition that the kidnapped soldiers were released, a cease-fire was in place and all sides agreed to the deployment.