BEIRUT — Hezbollah and its allies rose to a position of unprecedented dominance in Lebanon’s government yesterday, giving Syria and Iran, the militant group’s patrons, greater sway in the Middle East.

Lebanon Prime Minister Najib Mikati announced a new Cabinet dominated by Hezbollah and its allies after the country went five months without a functioning government. The move caps Hezbollah’s steady rise over decades from a resistance group against Israel to Lebanon’s most powerful military and political force.

Opponents of Hezbollah — which the United States considers a terrorist organization — say having it in control of Lebanon’s government could lead to international isolation. The group’s most ardent supporters are Iran and Syria, which dominated Lebanon for 29 years.

The new government opens the door for renewed Syrian influence in Lebanon at a time when the Syrian leadership is struggling at home. It’s a remarkable turnaround from 2005, when fallout from the assassination of former prime minister Rafik Hariri led to massive anti-Syrian protests in Lebanon.

The protests, dubbed the “Cedar Revolution,’’ drove tens of thousands of Syrian troops out of Lebanon and ended decades of Syrian domination over its smaller neighbor.

The ascendancy of Hezbollah is a setback for the United States, which has provided Lebanon with $720 million in military aid since 2006 and has tried in vain to move the country firmly into a Western sphere and end Iranian and Syrian influence. It also underscores Iran’s growing influence in the region at a time when Washington’s is falling.

Fadia Kiwan, a political science professor at Beirut’s St. Joseph University, said Hezbollah’s dominance in the new government could backfire on the group, which was formed in 1982 with Iranian support to fight Israel’s invasion of Lebanon.

“Such a government puts a great political responsibility on Hezbollah’s shoulders,’’ Kiwan told the Associated Press. “A moderate, national unity government would have offered more protection for the group.’’

The Islamic militant group’s power has been steadily growing over the years and its newfound clout could add volatility to a region already rocked by antigovernment uprisings in a half-dozen countries.

A Hezbollah-led government will raise tensions with Israel, which fought a devastating 34-day war against the Shi’ite militants in 2006 that left 1,200 Lebanese and 160 Israelis dead. Lebanon, torn apart by decades of civil war and deep sectarian divides, has had several major military conflicts with neighboring Israel.

Hezbollah forced the collapse of Lebanon’s previous, pro-Western government in January over fears it would be indicted by a UN-backed tribunal investigating the killing of Hariri, a billionaire businessman and political leader who had been trying to limit Syria’s domination of Lebanon in the months before his death.

Syria denied any involvement in his killing and called the tribunal a conspiracy by the United States and Israel.

Hariri’s son Saad, who was prime minister in January, refused to denounce the tribunal or cut off Lebanon’s 49 percent share of the funding for it.

Hezbollah and its allies then walked out of the government, forcing its collapse, and secured enough support in parliament to name Mikati as prime minister. But Mikati has struggled to form a Cabinet.

Yesterday, Mikati announced a Cabinet that gives Hezbollah and its allies 16 of the 30 seats. In the previous government, they had 10 seats.

The Cabinet still must be formally presented to Parliament for a vote of confidence.

The makeup of the new government is seen as almost entirely pro-Syrian. President Bashar Assad of Syria, facing a growing uprising against his rule at home, called twice to congratulate Lebanese leaders on the new government’s formation.

Lebanon’s politics are always fractious, in part because of the sectarian makeup of the country’s government. According to Lebanon’s power-sharing system, the president must be a Maronite Christian, the prime minister a Sunni Muslim, and the Parliament speaker a Shi’ite Muslim.

Each faith makes up about a third of Lebanon’s population of 4 million.

Talal Arslan, a politician from the tiny Druze sect, resigned yesterday after it was announced he was named to the post of state minister without portfolio. He said Mikati should have given representatives of the Druze community a higher-profile post. Mikati urged the Lebanese to give the government a chance to prove itself.

© Copyright 2011 Globe Newspaper Company.