UNITED NATIONS — Syria and Iran disagree on some issues regarding Lebanon, but they have a strong alliance that will be difficult to tear apart, an Israeli official said yesterday.

The official, who described intelligence assessments on condition of anonymity, detailed an unexpected rift between Syria and Iran in the growing dispute inside Lebanon over an international tribunal to try suspects in the assassination of a Lebanese prime minister, Rafik Hariri.

According to reports from Beirut, 70 members of Lebanon’s Parliament who support Prime Minister Siniora wrote a letter to the United Nations over the weekend calling for a new Security Council resolution based on the U.N. charter’s enforceable Chapter 7, which would force the split country to accept the tribunal.

A copy of the Lebanese parliamentarians’ letter reached the U.N. legal department last night, but Turtle Bay officials declined to comment on it.

Pro-Syrian factions in Beirut, who have expressed their strong opposition to the tribunal, fear that any international trial would expose top Damascus officials to international rebuke.

Immediate family members of the Syrian president, Bashar Al-Assad, were mentioned in U.N. investigations as possible suspects in the February 2005 Hariri assassination.

While Maronite Christian politicians, along with representatives of Palestinian Arabs and southern Lebanese Shiites, have expressed opposition to the tribunal, a large majority of the country supports it, according to polls.

The Israeli source said some Hezbollah officials, who are “reading the political tea leaves” inside Lebanon, advocate caution in resisting the tribunal. While blocking the tribunal is at the top of the agenda for Damascus, it is not as important for Tehran, which supports a conciliatory line on the tribunal, the Israeli source said.

Meanwhile, Syria has launched a charm offensive designed to coax Washington into negotiations that, according to Syrian opposition leaders, are mostly aimed at removing the threat of the international tribunal, which could bring down the Assad regime.

Yesterday, appearing on ABC’s “Good Morning America,” Mr. Assad said his country could be helpful to America in Iraq. In recent months, many in Washington have argued that Syria’s alliance with Iran is loose and that talks with the Assad regime could help to isolate Tehran.

“It is not in Syria’s long-term interest to be an ally of Iran,” Senator Webb, a Democrat of Virginia, said on the “Fox News Sunday” television program. “Syria and Iran have never been natural allies. They’re different ethnically. They’re different politically.”

However, the Israeli source who described the policy differences between the countries said Iran and Syria remain strong allies and that the idea of “peeling off” Syria from under Iran’s influence is not realistic at this stage.

This is also the assessment of Syrian dissidents who say Washington politicians are “naïve” to believe in such an imminent split between the two long-time allies.

“That’s an idea that the Saudis sold to the State Department six months ago,” the president of the Washington-based Reform Party of Syria, Farid Ghadry, said. “It will never happen.”

Mr. Ghadry said the Alawite sect ruling Damascus is an Islamic offshoot of Iran’s Shiism, which does make the two regimes natural allies.

In the Iran-Iraq war of the 1980s, the Syrian Baathists did not ally themselves with their political brethren in Baghdad but with the Iranian mullahs, Mr. Ghadry noted. “In the last few decades, Syria never went against Iran,” he said. “At the end of the day, all Assad wants is to end the Lebanon tribunal” that threatens his regime.