France's UN Ambassador Jean-Marc de La Sabliere announced the deal after deliberations among the council's 15 members that were overshadowed by the assassination of Lebanese Industry Minister Pierre Gemayel.
De La Sabliere told reporters that the long-awaited accord, enshrined in a letter to be sent to UN chief Kofi Annan, was reached hours before a 6:00 p.m. (2300 GMT) deadline set by council members on Monday.
His Qatari counterpart Nassir Abdulaziz al-Nasser, the lone Arab member of the council who earlier in the day asked for clarification of the text, confirmed the agreement.
"We are quite pleased at this outcome," US Ambassador John Bolton concurred.
The letter welcomed the conclusion of negotiations between the United Nations and the Lebanese government on the proposed tribunal in line with a Security Council resolution.
Council members decided that 51 percent of the expenses of the tribunal would be covered by voluntary contributions from member states and 49 percent by the Lebanese government.
"It is understood that the secretary general will commence the process of establishing the tribunal when he has sufficient contributions in hand to finance the establishment of the tribunal and 12 months of its operations plus pledges equal to the anticipated expenses of the following 24 months of the tribunal's operation," the letter said.
It said that should voluntary contributions be insufficient for the tribunal to implement its mandate, the UN secretary general and the Security Council "shall explore alternate means of financing the tribunal".
Diplomats said the tribunal blueprint would now have to be formally approved by the Lebanese parliament and ratified by the president with the agreement of the prime minister.
On Monday de La Sabliere said the council was wary of getting embroiled in the dispute over the constitutionality of the Lebanese cabinet's approval a week earlier of the UN document setting out the legal basis for the tribunal.
Lebanese President Emile Lahoud and other pro-Syria politicians expressed opposition to the move, and six pro-Syria ministers, including five Shiites, resigned November 11 after Siniora decided the cabinet would meet on the tribunal issue.
Lahoud, an ally of Syria, has said the cabinet's decision is "not binding for the Lebanese state" because it was taken by an "illegitimate" government. Meanwhile the council "unequivocally" condemned the Gemayel assassination and urged all parties in Lebanon and the region to show restraint.
"The Security Council welcomes the determination and commitment of the government of Lebanon, to bring to justice the perpetrators, organisers and sponsors of this and other assassinations and underlines its determination to support the government of Lebanon in its efforts to this end," the council said in a statement.

Copyright AFP (Agence France-Presse), 2006