France announced it was committing 1,600 more troops to the force, and the United Nations said a French general would keep command over the operation.
Jaques Chirac, the French president, said in a televised address on Thursday: "Two thousand French troops will thus be placed under the United Nations in Lebanon. France is ready, if the United Nations wishes, to continue commanding this force."
France initially offered to double its force in Lebanon to 400, disappointing many UN diplomats who had expected Paris to provide the backbone of the mission
After winning assurances from the UN that the troops would be able to defend themselves fully if they came under attack and could use force to protect civilians, Paris agreed to rethink its troop deployment.
French officials defended their caution, citing previous disastrous peacekeeping missions to Lebanon and Bosnia, where France lost dozens of men and felt hindered by restrictive UN terms of engagement.
"In a situation where everyone is weighing up the difficulty, France will assume its responsibilities in Lebanon," Chirac said.
"This force must be put in place but it must be based on a fair division of the troops. I have spoken to my colleagues to convince them to take on their share."
After France's initial offer, Italy promised up to 3,000 troops and offered to take command of the operation.
France led calls for a robust international force to safeguard the ceasefire and was criticised abroad for its initial, hesitant approach.
The UN has about 2,000 soldiers in Lebanon and wants to raise this number to up to 15,000 to police a shaky ceasefire that ended a month of fighting between Israeli forces and Hezbollah.
EU foreign ministers are due to meet in Brussels on Friday to discuss their response to the UN operation.