UNITED NATIONS — As the Lebanese presidential election approaches, politicians under threat of assassination could receive protection from U.N. troops already stationed in the country, the American ambassador to the United Nations, Zalmay Khalilzad, said.

Some diplomats yesterday compared the proposed reassignment of U.N. troops to protect Lebanese politicians to the role the security company Blackwater USA plays in Iraq. “We are not there yet,” Mr. Khalilzad told The New York Sun in explaining the idea put forth by certain members of the U.N. Security Council, including France and America, at the behest of some Lebanese politicians.

The Lebanese government would first have to request protection for its politicians, and the Security Council would need to approve such a role for the U.N. Interim Force in Lebanon, Mr. Khalilzad said. One of Lebanon’s leading politicians, Saad Hariri, did not make such a request during a meeting yesterday, an indication that the Lebanese authorities may be able to provide the necessary protection, Mr. Khalilzad added.

The governing coalition, led by Mr. Hariri’s party, known as the March 14 Alliance, has seen its majority in parliament eroded with the assassinations of some of its most prominent legislators. The killings began in February 2005, when Mr. Hariri’s father, Rafik Hariri, a former Lebanese prime minister, was slain in Beirut. Further assassinations cut into the majority of Christian, Druze, and Sunni legislators who won 72 seats in the 128-seat parliament in the elections that took place shortly after Hariri’s death. The latest victim was a member of the Christian Phalange Party, Antoine Ghanem, whose killing last month cut the majority bloc to 68 seats. The country’s opposition includes 59 pro-Syrian Shiite and Christian legislators, including some members of Hezbollah, which America considers a terrorist organization. The opposition says a two-thirds majority is needed to win the election to replace President Lahoud, whose term ends November 24. The assassination campaign is targeting members of the March 14 coalition, Mr. Hariri told reporters yesterday after a meeting with Secretary-General Ban. “When you have members of parliament sitting in a building to protect themselves from assassination,” he said, “I think this is unacceptable for the international community.”

UNIFIL, which is deployed in southern Lebanon, was reinforced with well-trained European troops after the war last summer between Israel and Hezbollah. Any change in its mandate to include protecting politicians would require the approval of all 15 members of the Security Council.

“The Security Council has a role in terms of holding those accountable responsible,” Mr. Khalilzad said. “Those who commit political assassinations will be brought to justice.”