* Annan's proposal to be discussed in Geneva on Saturday
* Unclear if Russia would accept exclusion of Assad (Adds background, diplomat)
By Louis Charbonneau
UNITED NATIONS, June 27 (Reuters) - Russia and other big powers have told mediator Kofi Annan that they support his idea of a Syrian national unity cabinet that could include government and opposition members but would exclude those whose participation would undermine it, envoys said on Wednesday.
Annan's proposal for a political transition aimed at ending the 16-month conflict in Syria is one of the main topics that Russia, the other four permanent Security Council members and key players in the Middle East will discuss at a meeting in Geneva on Saturday, diplomats told Reuters on condition of anonymity.
One diplomat summarized Annan's proposal, saying the Syria conflict can only end when all sides see a peaceful way to a shared future." Annan made clear it was "vital that (any) settlement (be) irreversible, (with) clear transition steps in fixed timeline," he said.
"These include establishing a transitional national unity government to create a neutral backdrop for transition," the diplomat said in his summary of Annan's plan.
"It could comprise present government members, opposition and others, but would need to exclude those whose continued participation or presence would jeopardize the transition's credibility, or harm prospects for reconciliation and stability."
The diplomat added that the idea of excluding certain people was clearly referring to Syrian President Bashar al-Assad, though Annan's proposal does not explicitly say Assad could not serve in a national unity government. That gives Russia the option of insisting that Assad be allowed to stay in power.
"The Russians signaled to Annan that they accept his transition plan," he said. Several Western diplomats confirmed his remarks, adding that all five permanent veto-wielding U.N. Security Council members backed it.
Another diplomat said Russia's acceptance of Annan's proposal, which he circulated to the five permanent Security Council members this week, did not mean it has abandoned Assad.
"I'm very skeptical," he said. "I don't see the Russians giving up on Assad."
The Russian mission at the United Nations was not available for comment.
SHIFT IN RUSSIA'S STANCE?
Annan made acceptance of his guidelines for a political transition for Syria a condition for organizing Saturday's meeting, which will include the United States, Britain, France, Russia, China, Turkey, Iraq, Kuwait and Qatar. It will not include Iran or Saudi Arabia.
Russia has repeatedly said its supports Annan's idea of creating a "contact group" of powerful nations and regional players with influence on the Syrian government or the opposition to push for an end to the violence in Syria.
Several diplomats said Russia's acceptance of Annan's proposal appeared to signal a shift in its stance on Syria. But it was not immediately clear if Moscow's support for the idea of a national unity government in principle meant that it was now abandoning Assad, a staunch ally and key Russian arms purchaser.
The United States, Britain and France have said that Assad is responsible for the violence, which the United Nations estimates has killed at least 10,000 people, is no longer fit to govern. Russia and China, however, reject what they describe as Western calls for "regime change."
Russia has repeatedly said it is not insisting that Assad must remain in power at all costs, but that any decision on whether or not he should step down should come from the Syrian people, not from outside pressure or military intervention, as happened last year in Libya.
Saturday's meeting, which Russian Foreign Minister Sergei Lavrov and U.S. Secretary of State Hillary Clinton will attend, will have to agree on the details of the political transition and the mechanisms for implementing it, diplomats said.
Annan, a former U.N. secretary-general, also wants Saturday's meeting to revive his moribund six-point peace plan that has failed to end the fighting between Assad's forces and an increasingly militarized opposition. The conflict has escalated in recent weeks.
Annan said the aim of the one-day talks was to identify measures to secure full implementation of his stalled peace plan and Security Council resolutions, including an immediate halt to all violence. (Additional reporting by Arshad Mohammed in Washington.; Editing by Sandra Maler and Christopher Wilson)