Karami, who had continued to lead a caretaker government, immediately invited the opposition to join him in a national unity government. He said he will begin consultations early next week with lawmakers to form a Cabinet.
"The difficulties we all know cannot be confronted without a government of national unity and salvation," he said. "We will extend our hand and wait for the other side."
But the opposition, who orchestrated the protests that led to Karami's Feb. 28 resignation, rejected the reappointment even before it became official.
They have complained that the national unity proposal was a trap to bring opposition members into the Cabinet without giving them a say in policymaking.
Karami suggested he might not proceed if he fails in bringing to bring all factions together.
"If there is no national unity government and if I am the obstacle then I am ready to bow out," he said.
Karami's return to leadership ensures Damascus' continued dominance in Lebanon's politics.
Syria is keen to keep its hold on Lebanese decision-making as it pulls its forces back to the smaller country's eastern Bekaa Valley and negotiates with the Beirut government on the troops' full removal at a later date. Lebanese officials have said the first phase pullback, including of Syrian intelligence, would be completed by March 23.
Syrian troop redeployment was picking up pace as soldiers evacuated positions in the north and center of the country. Long convoys of dozens of Syrian trucks and buses headed east on mountain roads late Wednesday and Syrian soldiers evacuated in convoys most of their positions in the northern port of Tripoli and two hilltop positions overlooking Lebanon's second-largest city.
Syrian President Bashar Assad decided to call the troops home after three difficult weeks, with the international community and even close Arab friends Egypt and Saudi Arabia forcefully demanding that the Syrian army withdraw from Lebanon.
U.N. Secretary-General Kofi Annan called on Syria to carry out a full withdrawal of its 14,000 troops from Lebanon and said he was sending an envoy to the region to discuss a pullout.
President Bush on Wednesday kept up the intense campaign against Damascus, saying Wednesday that Syria's withdrawal plans in Lebanon are just a "a half measure" and that Syrian intelligence services exercise "heavy handed" influence in Lebanon's government.
Karami called for political dialogue and said he will try to form a Cabinet that includes all factions. He warned of "unforeseen dangerous results" to Lebanon's economy if the political vacuum and street protests persist.
"Therefore, I call on every one of all national forces to take part in a national dialogue on the table of the Cabinet and I am not putting any conditions," he said. "I will not form a Cabinet of one color."
Opposition member Samir Franjieh on Wednesday described a reappointment of Karami as a government escalation aimed at scuttling any attempts at dialogue.
"It is a step that greatly challenges the opposition and the people's feelings," said Franjieh. He did not say how the opposition plans to react.
The decision by the pro-Syrian President Emile Lahoud came after legislators, ignoring weeks of popular anti-government protests, advised the president during consultations Wednesday to rename Karami. He was virtually assured nomination after 71 of 78 legislators put forward his name, more than half of the votes required in the 128-member legislature.
Under the constitution, the president is obliged to comply with the choice of the majority of legislators.
Karami rejected suggestions that his reappointment was inspired by Syria, saying his supporters had the majority in the parliament and with the people, a reference to Tuesday's Hezbollah-organized rally in which hundreds of thousands of pro-Syrian supporters participated.
"It was a massive demonstration that asserted our legitimacy in the Lebanese street," he said.
But pan-Arab newspaper Al Hayat commented Thursday that Karami's reappointment was a "farce," wondering why the insistence on Karami.
"His staying in the same position is the first signal that those who make appointments in Lebanon are still the same and there is still no Lebanese will to change such tradition, which has hurt Syria as much as it has hurt Lebanon," wrote Abdul-Wahab Badrakhan, deputy editor of the respected London-based daily.
Karami's previous Cabinet, which governed from late October until he resigned in parliament Feb. 28, was among the most pro-Syrian government Lebanon has seen since the end of the 1975-90 civil war. U.S. officials had described Karami's Cabinet as "Made in Syria."
Karami said Thursday his new government will oversee the investigation into the Feb. 14 assassination of former Premier Rafik Hariri in order to find the culprits and "hand down the punishment they deserve."
Hariri's assassination, which the opposition blames on the Lebanese government and Syrian backers, was the catalyst for anti-Syrian protests in Lebanon and the increased international uproar against Syria. Both governments have denied involvement.