Lebanese Prime Minister Rafiq Hariri resigned Wednesday in a sign of deepening divisions within Lebanon's fragile government over the decisive role that Syria, a larger and powerful neighbor, plays in Lebanon's political life.

Hariri, one of Lebanon's leading postwar political figures, submitted his resignation to President Emile Lahoud, dissolved his cabinet and said he would not form the country's next government. He will return to parliament, where he helps lead a bloc of Christian and Muslim legislators increasingly opposed to Lahoud, a Maronite Christian whose term in office was extended last month under pressure from the Syrian government.

Hariri's resignation poses a new test for Lebanon's postwar constitution, which distributes power among the country's Christian president, Sunni Muslim prime minister and Shiite Muslim speaker of parliament. Lahoud must now hold talks with parliament to select a new cabinet, and Hariri's successor must be another Sunni. But many Sunnis have opposed Lahoud since he accepted the term extension.

Hariri stepped down as there is growing international pressure on Lebanese politicians to more forcefully turn against Syria's long-standing presence in their country. Although his departure was not entirely unexpected, it will likely deepen the perception that Lebanon, which is among the Middle East's most economically vibrant and socially progressive countries, has entered a period of political tumult. The billionaire real estate tycoon has been a reassuring symbol to Lebanon's international lenders and potential investors because the fiscal program he favored called for budget cuts and privatizations to help reduce the country's heavy debt.

Hariri gave no official reason for his resignation, but he suggested in an interview this month that if he left the government, it would be over differences with the president regarding Syria's influence in Lebanese politics.

"I want Lebanon to be democratic, not only by respecting free speech, human rights and elections, but also respecting international law and acting as part of the international community," Hariri said during the interview at his palatial home. "Lebanon is still a democratic country, but we are trying to solve our own problems."

Syria has maintained roughly 20,000 troops in Lebanon since the early days of the civil war, which ended in 1990 with a power-sharing agreement between rival Christian and Muslim militias. The soldiers and an extensive intelligence network have emerged over the years as instruments of Syrian power in Lebanon, but their presence has been increasingly opposed by many Lebanese.

Last month, parliament voted to grant Lahoud, the former head of the army, a three-year term extension. The move was made under pressure from President Bashar Assad of Syria, who, according to Western diplomats and political analysts, may have worried that the Lebanese presidential election scheduled for November would undermine Syrian influence.

Moving unsuccessfully to head off the term extension, the U.N. Security Council approved a resolution in early September calling for "all foreign troops" to be removed from Lebanon -- a not-so-tacit reference to Syria. The resolution also requested that Syrian-sponsored militias operating in southern Lebanon be disarmed. U.N. Secretary General Kofi Annan reported this month that no progress had been made on the resolution, which was sponsored by the United States and France.

The Security Council issued a statement Tuesday reiterating its demands and calling for semiannual status reports from Annan on the matter. At the same time, several U.S. lawmakers have urged President Bush to freeze the assets of Lebanese and Syrian officials until the terms of the resolution are met.

The proposal alarmed Hariri, who has vast real estate, computer and investment holdings in the United States and other countries. He summoned the U.S. ambassador in Beirut to a meeting last week to express his concern.

The ambassador, Jeffrey Feltman, told reporters after the meeting that freezing assets was only an "idea." But, Feltman added, "the proposal does reflect the very strong concern within the U.S. Congress about supporting the full independence and sovereignty of the Republic of Lebanon."

Rafiq Hariri, who gave no official reason for his resignation, has been one of Lebanon's leading postwar political figures.