UNITED NATIONS – In a move that could carry broad implications for Lebanese politics and the country’s struggle to escape Syrian influence, the U.N. Security Council yesterday stopped short of fully endorsing a request by Prime Minister Siniora to expand international intervention there.

In a unanimous decision, however, the council set in motion a process to “provide assistance” for the Lebanese government in its investigation of a spate of political assassinations in the country. It also acknowledged the government’s request to establish an international tribunal that would try those found guilty in the February 14 killing of a former Lebanese prime minister, Rafik Hariri.

The resolution also extended the mandate of the existing international probe of the Hariri murder until June, and expressed “extreme concern” that Syria had not yet provided U.N. investigators with “full and unconditional cooperation.” It did not, however, repeat past threats to impose sanctions on Syrian individuals involved in the murder.

“We are making it clear to the government of Syria they can’t run, they can’t hide,” America’s ambassador to the United Nations, John Bolton, said. Although the final vote was on a resolution that fell short of fully endorsing the Lebanese government’s request, Mr. Bolton said, “My understanding is Prime Minister Siniora is fully content with the language in the resolution. I think he should be.”

On Tuesday, Mr. Siniora requested in a letter to Secretary-General Annan that he ask the council to establish an international tribunal to try Hariri’s killers, and expand the mandate of the Hariri investigation to include other assassinations since October 2004.

Mr. Bolton said that the outgoing chief of the commission investigating Hariri’s death, Detlev Mehlis, told the council that expanding the investigation to include a host of other murders would require increased resources. The council, Mr. Bolton said, was therefore unable to endorse Mr. Siniora’s request completely.

Under pressure from council members who are more sympathetic to Syria, specifically Russia, a French draft for a resolution that fully backed the expansion of the international investigation was watered down. The final resolution requested that the secretary-general, “in consultation with the commission and the Lebanese government” study whether such expansion is possible.

Some diplomats wondered yesterday whether the compromised language would register as a victory for Mr. Siniora in Lebanon, where his move to further involve the council in investigating political assassinations created turmoil. Five Shiite, pro-Syrian Cabinet members threatened to quit Mr. Siniora’s government.

“The Security Council has positively answered his request as far as was possible today,” said the French ambassador, Jean Marc de la Sabliere, when asked by The New York Sun whether the qualified council endorsement would be enough for Mr. Siniora. “We have received that request two days ago and we have taken [it] into account. I hope the Lebanese government will be satisfied.”

Before the council vote yesterday, Mr. Siniora’s government was described by the local press as “on the verge of collapse.” The five Cabinet ministers from the pro-Syrian Shiite terrorist parties Hezbollah and Amal said they would boycott yesterday’s Cabinet meeting. “We stand by our decision,” Energy Minister Mohammed Fneish, of Hezbollah, told the English language Daily Star.

Arab leaders, including President Mubarak of Egypt, the Arab League’s secretary-general, Amre Moussa, and the Saudi ambassador to Lebanon, Abdul Aziz Al-Khoja, tried to mediate between Lebanon and the Baathist government in Damascus. The usually united Arab group at the United Nations was forced to choose between two of its members.

“I support the Lebanese request for further assistance from the U.N. Security Council,” the outgoing Algerian ambassador, Abdallah Baali, told the Sun, but “I try to accommodate everybody. I want Syria to be treated fairly.”

According to diplomats who described the consultations inside the council on condition of anonymity, however, Mr. Baali helped the American, French, and British sponsors of the resolution by signaling early on that after some amendments he would support the Lebanese request.

His signal left Russia in a position to remain alone in protecting Syria against the widening outside involvement that had increasingly left the Assad regime isolated. “We continue to oppose unwarranted pressure on Damascus,” Russia’s U.N. ambassador, Andrey Denisov, told the council. He told the Sun he was satisfied with the resolution.