WASHINGTON — The authority of peacekeeping forces in southern Lebanon is a matter of annual debate at the United Nations, pitting security concerns against sovereignty rights. But for the first time in recent memory, the Security Council this year will formally review the size of the forces and allow cuts to be considered when it renews the mission, three officials said on Wednesday.

The issue will be put to the Security Council in a vote on Thursday to extend the United Nations Interim Force in Lebanon, known as UNIFIL, for another year. A draft of the final agreement, which includes the force reduction review, was described to The New York Times on the condition of anonymity.

It is a small but significant concession to American and Israeli diplomats who have for years said the peacekeepers should more aggressively investigate and report Hezbollah activity in southern Lebanon, near the Israeli border. Because the United States and Israel do not believe the peacekeepers have carried out their duties as fully as possible, the countries have pushed for fewer forces, in part as a cost-cutting measure.

Hezbollah, which is backed by Iran, is a political party represented in the Lebanese government as well as a formidable military force. The United States considers Hezbollah a terrorist organization.