UNITED NATIONS — The pitfalls of Lebanon’s position as president of the United Nations Security Council were visible today, as the Beirut representative, who presided over a periodic council debate on international terrorism, clashed with Israel’s ambassador over Hezbollah’s definition as a terrorist group.

At Turtle Bay, where Iran recently joined the committee to defend the rights of women and where Libya is a shoo-in for membership in the top body dealing with human rights, little stir is created when a country under the sway of Hezbollah is serving as the president of the world body’s most prominent institution.

In today’s meeting, the 15 council members as well as some non-members who have asked to join the “open debate” discussed how terrorism poses a threat to the world. Technically, the meeting was convened to review the work of several committees established by the council in the aftermath of the September 11, 2001.

“The most dangerous terrorist organizations threatening Israel’s security are Hamas in the south and Hezbollah in the north,” Israel’s ambassador here, Gabriela Shalev, said as she joined the debate, adding that it was “alarming” that several United Nations member states support and harbor such terror organizations.

Stung by a clear reference to her country, Lebanon’s deputy ambassador, Caroline Ziade, called Ms. Shalev’s remark “unfortunate.” Closing the debate, Ms. Ziade said she wanted to speak not as the council’s rotating president for the moth of May, but in her national capacity. Hezbollah, she insisted, is not a terrorist organization. It is a “legitimate party” represented in the Lebanese parliament

“We regret that the name of Hezbollah was used in our debate,” Ms. Ziade said, adding that Ms. Shalev tried to “derail the debate from its course.” Israel, the Lebanese ambassador added, is “a neighbor that continues to aggress [against] its neighbors. This is why we should differentiate between terrorism and the legitimate right to resist against foreign occupation.”

Hezbollah has been prominent on the State Department’s list of terrorist organizations ever since its inception in the 1980s. Even as the European Union and the United Nations decline to define it as a terror group, many Western security analysts — and every administration since President Reagan’s — consider the Iranian-controlled Hezbollah the second most dangerous international terror organization behind al-Qaeda.

But since the formation of a wide-coalition Lebanese government, Hezbollah can practically veto any decision the country takes. So beyond the dispute over the terror designation, Hezbollah’s voice in Beirut makes it difficult for Lebanese diplomats to seriously work on several of the gravest issues on the agenda of the Security Council.

America and several European countries approached Lebanese officials last year, prior to the General Assembly’s approval of the country as the Arab representative on the Security Council, asking about Beirut’s position on Iran sanctions. According to several diplomats who spoke on condition of anonymity, Prime Minister Hariri’s government promised it would abstain in an Iran vote,  virtually excusing itself from participating in deliberations over a new round of sanctions on Iran.

Lebanon’s envoy here, Nawaf Salam, denied the account, telling the Sun recently that his country would make a decision “according to our national interest.” But several Western diplomats acknowledged that one of the reasons that the sanction negotiations were deferred to next month was the fear that imposing new punitive measures on Iran during Lebanon’s presidency could undermine the delicate political balance in Beirut.

The issue of Iran is only one of the challenges that the U.N.’s most prominent body has faced ever since Lebanon joined it in January. The Security Council is charged with defusing disputes that pose a threat to international peace and security. Lebanon, where Hezbollah’s arsenal is growing by the day, could soon find itself in the midst of precisely such a dispute.

Last month’s reports on delivery to Hezbollah via Syria of sophisticated Iranian-made missiles have raised fears that the region would soon be thrown yet again into war. But the Security Council is unlikely to take that topic during Lebanon’s presidency, because many diplomats would consider such a topic too sensitive.

Tiptoeing around Lebanon is likely to continue next month, when Mexico is scheduled to replace it as the rotating council president — and for the rest of the country’s two-year council membership.

“To use an old Yiddish phrase, if it wasn’t my child, I would laugh, too,” Ms. Shalev told me after today’s council meeting. She was referring to a punch line to an old joke about an ironic situation that nevertheless is too precarious to consider as laughing matter.