* Opposition says Alkhatib will meet senior U.S. and Russian officials
* But Russia says no meeting currently in Lavrov's schedule
* Alkhatib fights off internal challenge after talks offer
* Question of Assad's departure divides U.S., Russia, opposition
By Khaled Yacoub Oweis
AMMAN, Feb 1 (Reuters) - A leading Syrian opposition source said the opposition would meet officials from the United States, Russia and the United Nations in Munich on Saturday to discuss a political transition for Syria.
If confirmed it would be the first time that the United States and Russia, key players who have been at loggerheads over whether President Bashar al-Assad can have a role in a transitional government, had sat down together with the opposition. However, Russia's deputy foreign minister declined to confirm the proposal.
Syrian National Coalition officials said on Friday that Coalition president Moaz Alkhatib would meet U.S. Vice President Joe Biden, Russian Foreign Minister Sergei Lavrov and U.N. envoy Lakhdar Brahimi on the sidelines of the Conference on Security and Cooperation in Europe in Munich.
"Alkhatib was informed by Brahimi that it will be a four-way meeting. He is going to Munich alone," a high-level Coalition member told Reuters.
"I think Russia warmed to the meeting after Alkhatib's proposal (to talk to Syrian officials). The Coalition has adopted a position of constructive vagueness on whether Assad should step down first for a transition to happen, and it has stirred things up," the Coalition member said.
But shortly afterwards, Russian Deputy Foreign Minister Gennady Gatilov sent a tweet saying: "As it stands today, there is no such meeting mentioned in the programme of the Russian Foreign Minister."
Alkhatib had to fight off an overnight challenge to his authority after saying he would be willing to talk to Syrian officials without Assad stepping down first, but that concession appeared to have opened the way to Saturday's talks.
Both the Coalition and the armed opposition inside Syria had been saying they would be willing to discuss a political transition only after Assad left power.
Washington backed the position, while Moscow, Assad's main backer, was adamant that his departure could not be a precondition for talks, paralysing international efforts to end a 22-month-old conflict that has already killed more than 60,000.
A meeting of the Coalition's 12-member politburo ended at 5 a.m. on Friday with the leadership instructing Khatib, a Sunni preacher from Damascus, not to respond to any proposals made in Munich before reverting to them.
STRATEGY FOR PEACE OR WAR
The source said the Coalition's politburo had elected a committee to draft a political manifesto that set a strategy for peace, "or advancing the war" if international efforts fail to negotiate an exit for Assad.
The structure of the 70-member Islamist-dominated coalition, which was formed with Western and Arab backing in December, makes Alkhatib a first among equals rather than an outright leader.
The source said "knives were out for Alkhatib" from Islamists on the politburo and from the Syrian National Council, an opposition group superseded by the Coalition, after he said he was willing to sit with Syrian officials to discuss a transition if Assad freed tens of thousands of political prisoners arrested since the revolt began.
Kamal al-Labwani, a secular leader and long-time political prisoner, called Khatib's remarks a fatal mistake that bestowed legitimacy on Assad and would hurt the morale of the revolt.
Alkhatib said his offer of talks had been motivated by the plight of the prisoners, many of whom were in secret police dungeons, and made clear that he still believed Assad and his cohorts must eventually leave.
Another Coalition leadership source told Reuters the politburo had agreed that Alkhatib "would demand at the meeting, and accept nothing less than, the ouster of Assad and the whole secret police state and international support to rebuild Syria as a democracy".
A Western diplomat in contact with the Syrian opposition said the Munich meeting had to present Alkhatib with proposals for the removal of Assad that he could accept without losing his credibility.
"The level of frustration among the opposition with lack of international support for the revolt is very high," the diplomat said. "We may be seeing one of the last chances before the opposition says: 'To hell with the international community, and let's direct all our efforts toward war'."
U.S. Secretary of State Hillary Clinton urged Assad's allies Iran and Russia on Thursday to rethink their positions, saying the most dire scenarios of the conflict spilling beyond its borders could still come to pass. Already more than 700,000 Syrians have fled into neighbouring countries.
She told reporters there were signs that Iran was sending more people and increasingly sophisticated weaponry to support Assad's war, in which he has lost swathes of rural areas but managed to hold on to the central parts of most major cities.
"I personally have been warning for quite some time of the dangers associated with an increasingly lethal civil war and a potential proxy war," Clinton told a small group of reporters a day before she is replaced by Senator John Kerry.
"Therefore, I think it's incumbent on those nations that have refused to be constructive players to reconsider their positions because the worst kind of predictions of what could happen internally and spilling over the borders of Syria are certainly within the realm of the possible now."
Western support for the uprising has been mostly limited to political rhetoric denouncing Assad and humanitarian aid, despite pleas from rebels for arms.
Britain's call to amend a European Union embargo on arms sales to Syria to help Assad's opponents met opposition on Thursday when EU governments warned it could allow weapons to end up in the wrong hands, including Islamist units.
On Wednesday, Israeli jets struck what Syria said was a military research centre and diplomats said was a weapons convoy heading for Lebanon.
Syria warned of a possible "surprise" response. Lebanese residents reported that Israeli war planes were flying in Lebanese airspace on Friday, a common occurrence but more sensitive after the strike on Syria. (Writing by Oliver Holmes; Editing by Kevin Liffey)