* Government delegation to head home unless "serious work" starts by Saturday
* Opposition demands government accept transition before meeting
* Talks would be the first in three-year war
By Khaled Yacoub Oweis and Stephanie Nebehay
GENEVA, Jan 24 (Reuters) - Syria's first peace talks were on the verge of collapsing on Friday before they began, with the opposition refusing to meet President Bashar al-Assad's delegation and the government threatening to bring its team home.
The opposition said it would not meet Assad's delegation unless it first agreed to sign up to a protocol calling for a transitional administration. The government rejected the demand outright and said its negotiators would return home unless serious talks began within a day.
"If no serious work sessions are held by (Saturday), the official Syrian delegation will leave Geneva due to the other side's lack of seriousness or preparedness," Syrian state television quoted Foreign Minister Walid al-Moualem as saying.
Friday was meant to be the first time in three years of war that Assad's government and foes would negotiate face to face.
But plans were ditched at the last minute after the opposition said the government delegation must first sign up to a 2012 protocol, known as Geneva 1, that calls for an interim government to oversee a transition to a new political order.
"We have explicitly demanded a written commitment from the regime delegation to accept Geneva 1. Otherwise there will be no direct negotiations," opposition delegate Haitham al-Maleh told Reuters.
The government delegation met U.N. envoy Lakhdar Brahimi separately, and said it rejected the opposition demand: "No, we will not accept it," Information Minister Omran Zoabi told Reuters.
Brahimi, who met the government team for barely an hour, was due to talk to the opposition delegation separately later on Friday.
The opposition says it has come to discuss a transition that will remove Assad from power. The government says it is there only to talk about fighting terrorism - the word it uses for its enemies - and that no one can force Assad to go.
"There are no Syrian-Syrian talks at the moment," said U.N. spokeswoman Alessandra Vellucci. "I cannot tell you anything about what will happen in the next few days."
Even before the announcement that the direct talks were cancelled, the outlook was dim.
"The objective is for the first round of talks to last until next Friday, but expectations are so low we'll see how things develop day by day," a Western diplomat said.
"Every day that they talk is a little step forward."
Brahimi has indicated that his aim is to start by seeking practical steps, like local ceasefires, prisoner releases and access for international aid deliveries, before embarking on the tougher political negotiations. But even those narrow aims would fail if the delegations go home.
Syria's civil war has already killed at least 130,000 people, driven up to a third of the country's 22 million people from their homes and made half dependent on aid, including hundreds of thousands cut off by fighting.
Among the hurdles to progress, the Islamist militants who control most rebel-held territory are boycotting the talks and say anyone attending negotiations that fail to bring down Assad would be traitors.
Assad's main regional backer, Iran, is also not represented at the Geneva talks. U.N. Secretary-General Ban Ki-moon invited Tehran at the last minute, but then withdrew the invitation 24 hours later when it refused to endorse the Geneva 1 protocol.
During Wednesday's opening ceremony, the government delegation drew a rebuke from Ban for using inflammatory language after referring in a speech to rebels raping dead women, ripping foetuses from the womb and eating human organs.
In a defiant speech on Thursday, opposition leader Ahmed Jarba said the international community had concluded that Assad cannot stay in power.
"We have started to look into the future without him. Assad and all of his regime is in the past now," he said.
"Nobody should have any doubt that the head of the regime is finished. This regime is dead."