UNITED NATIONS — A battle for a U.N. Security Council seat traditionally reserved for an Arab state is heating up between Western-friendly Mauritania and America’s old nemesis Libya.

The Security Council recently removed sanctions imposed on Libya after the 1988 terror bombing of Pan Am flight 103 over Lockerbie, Scotland. Libya also agreed to dismantle its nuclear program and is now seeking to cash in, launching a drive to gain one of the two-year seats on the council, diplomats said.

America has concerns about the erratic behavior of Libya’s leader, Colonel Muammar Gadhafi, however, and has led a campaign to prevent Libya from obtaining a council seat.

In 2004, America backed Algeria’s candidacy over Libya’s; it was not clear yesterday whether America or other Western countries were behind Mauritania’s bid.

Mauritania, which in March conducted its most democratic election to date, yesterday sent a letter to the secretary-general’s office that deals with General Assembly affairs to officially launch its campaign to become one of the 10 elected council members. The Arab council seat traditionally rotates between Asian and African countries; the current occupant is Qatar, meaning the next should be a North African country.

Several diplomats said yesterday that Morocco might offer its candidacy for the seat. But the Moroccan ambassador to the United Nations, El Mostafa Sahel, said his country currently has no plans to contest the seat. The North African group at the General Assembly is trying to coalesce around an agreed-on candidate, Mr. Sahel said.

“It is time,” the Mauritanian ambassador to the United Nations, Mohamed Ould Tolba, told The New York Sun. Mr. Tolba’s letter yesterday made his country’s case more specifically: “The Islamic Republic of Mauritania was, for one time, a member of the Security Council from 1974 to 1975,” Mr. Tolba wrote. “All the other states of the North Africa region got the opportunity to be members of the Security Council after this period.”

Representatives from the Libyan mission were not available for comment.

America and the four other permanent members of the Security Council consider it to be a serious actor on the world stage, in contrast to other U.N. bodies, and at times they have exerted pressure on the council’s regional groups. Last year Venezuela was blocked from becoming a member.

Libya’s candidacy for the council has been blocked several times in the past, even as America declined to oppose membership for such countries as Syria, which was elected to the council in 2002. American officials yesterday declined to say what they would do about Libya’s current candidacy.

“We would look seriously at any candidate” from North Africa, a spokesman for the American mission to the United Nations, Benjamin Chang, said. He added, however, “As we tackle key challenges such as Darfur, Iran, and Lebanon, we are looking for a responsible candidate that would uphold the principles of the Security Council.”

Mauritania maintains “a good relationship with the United States, and we also have diplomatic relations with Israel,” Mr. Tolba said, adding that Colonel Gadhafi has heaped scorn on the Security Council in the past.

“If a country is not a superpower and has no nuclear capabilities, it cannot use its right at the Security Council even if it is given a permanent seat,” the Libyan ruler said in a televised speech in 2005. “The powerful and nuclear states are the ones who lead the Security Council and give themselves permanent seats at the Security Council. They are laughing at us.”