GENEVA — Representatives of global powers and Middle East countries gathered in Geneva on Saturday to try to find a political solution for ending the violence in Syria and settle differences over the role of President Bashar al-Assad.

At a preparatory round of discussions on Friday, Kofi Annan, the United Nations and Arab League special envoy who called the meeting, said he was optimistic of success. But heavy civilian casualties in fighting in Syria on Friday underscored the challenge that he faces in trying to salvage a cease-fire plan agreed to three months ago but never fully put in place while also winning support for a political transition plan on which Russia and China remain at odds with the United States and other Western countries.
Mr. Annan’s guidelines call for a government of national unity with full executive powers that he says could include members of the present government but would exclude “those whose continued presence and participation would undermine the credibility of the transition and jeopardize stability and reconciliation.” That wording implies the exclusion of Mr. Assad, opening up the issue of regime change in Syria that lies at the heart of differences between the United States on one side and Russia and China on the other.
After meeting for three hours Friday in St. Petersburg, Russia, Secretary of State Hillary Rodham Clinton and her Russian counterpart, Sergei Lavrov, emerged without apparently bridging their differences. The United States has said that Mr. Assad’s brutal response to opposition in Syria has undermined its legitimacy and that he must step aside as part of any solution. Russia, Mr. Assad’s most important ally, may not rule out his departure, diplomats in Geneva said, but insists that it is an issue Syrians must decide for themselves.
Mr. Lavrov said after his talks with Mrs. Clinton that he believed the United States had softened its position and was more accepting of Russia’s views. “I heard a very experienced diplomat, an experienced politician, who said that she understood our position,” he said, referring to Mrs. Clinton. “We have a very good chance to find common ground at the conference in Geneva tomorrow.”
American officials took a more cautious line. “There are still areas of difficulty and difference,” a State Department official told reporters. Out of respect for Mr. Annan, American officials had agreed they should go to Geneva to try and produce a result, the official added. “We may get there, we may not.”
The preparatory talks in Geneva on Friday also appeared to have made little headway. “It’s looking bad, it’s getting worse,” an Arab diplomat attending the talks told Reuters as the meeting ended.
Arriving at the meeting on Saturday, the British foreign secretary, William Hague said participants needed to “to approach today’s discussions with a sense of great urgency and responsibility.”
“The situation in Syria is only getting worse,” Mr. Hague said. “The number of deaths yesterday alone was absolutely horrific.”
Saturday’s meeting included senior officials from the United States, Russia and China, along with Britain and France, all permanent members of the United Nations Security Council. Participants from the region included foreign ministers of Turkey, Iraq, Kuwait and Qatar.
The meeting came about only after sharp disagreement on who should attend. Conspicuously absent was Iran — a crucial ally of Mr. Assad, whose participation was blocked by the United States and its allies — as well as Saudi Arabia, a strong supporter of Syrian opposition groups, and Jordan, which borders Syria.
Mr. Hague said 9 of the 11 delegations attending are in agreement with the proposals, but added “we haven’t reached agreement in advance with Russia and China. That remains very difficult. I don’t know whether it will be possible to do so.”
Gennady Gatilov, the Russian deputy minister of foreign affairs, said early Saturday that the officials had deadlocked on a draft proposal. “Our Western partners want to determine the results of the political process in Syria themselves, though this is a matter only for the Syrians, and they are the ones who should do it,” he wrote on Twitter.
Even if diplomats achieved an accord, the escalation in violence in Syria since the cease-fire plan three months ago has exposed the difficulty of translating international agreements into action.
Opposition groups tracking casualties in Syria said on Friday the fighting in the previous 24 hours had been the deadliest of the year, with estimates of civilian casualties varying between 125 and 139, many of them in the Damascus suburb of Douma.
Mr. Assad, in an interview broadcast on Iranian television this week, made clear his opposition to any arrangement brokered abroad. “We will not accept any non-Syrian, nonnational model, whether it comes from big countries or friendly countries,” Mr. Assad said. “No one knows how to solve Syria’s problems as well as we do.”
But Mr. Annan has made clear that competing agendas had limited the possibilities for pressuring the Syrian government and the opposition into implementing a cease-fire. In an op-ed article in The Washington Post on Friday, Mr. Annan left no illusion about the possible consequences if the international community failed to come together in Geneva. “The downward spiral will continue — and may soon become irreversible,” he wrote.