LONDON — As John Kerry arrived at his first stop on his maiden trip as the United States secretary of state, American officials were struggling on Sunday to salvage an important meeting with the Syrian opposition.
Mr. Kerry and foreign ministers from Europe and the Middle East are scheduled to meet in Rome on Thursday with opponents of President Bashar al-Assad of Syria, including Sheik Ahmad Moaz al-Khatib, who leads the opposition. But they are threatening to boycott the conference to protest what they see as fainthearted international support.
To try to rescue the meeting, Robert S. Ford, the American ambassador to Syria and chief envoy to the opposition, was sent to Cairo on Sunday to implore opposition leaders to attend the session in Rome.
“The Syrian opposition leadership is under severe pressure now from its membership, from the Syrian people, to get more support from the international community,” said a senior administration official who was traveling on Mr. Kerry’s plane. “And in that context, there’s quite a bit of internal discussion about the value of going in international conferences.”
The issue upset the first day of a carefully choreographed trip that is intended to introduce Mr. Kerry as the chief American envoy and to give a lift to the diplomatic stalemate on Syria. Mr. Kerry, who took office this month, is traveling to Britain, Germany, France, Italy, Turkey, Egypt, Saudi Arabia, the United Arab Emirates and Qatar over 11 days.
Even before his trip was formally announced, Mr. Kerry raised expectations by saying he had new ideas on how to change Mr. Assad’s calculations that he could remain in power.
Mr. Kerry has not publicly explained the proposals, but they appear to include marshaling support from Russia, which has been providing arms and financial help to Mr. Assad. Toward that end, Mr. Kerry plans to meet in Berlin on Wednesday with Sergey V. Lavrov, Russia’s foreign minister.
The meeting with the Syrian opposition is to be hosted by Italy. Last week, the European Union agreed to extend its embargo on weapons shipments to Syria for another three months, a move that precludes European arms shipments to the opposition.
But the European Union did agree to a British proposal that nonlethal assistance be expanded. As a result, body armor, night-vision goggles, armored vehicles and other equipment can be sent to armed opposition groups in Syria, an American official said.
So far, the Obama administration has not gone that far in its support. While the United States provides nonlethal assistance like computers and radios to the opposition, it has not been willing to provide nonlethal aid to armed factions within Syria, an approach that experts say has limited its influence with these groups.
State Department officials traveling with Mr. Kerry declined to discuss whether the United States would soon be prepared to take that step.
President Obama rebuffed a proposal last year from the State Department, the Pentagon and the C.I.A. that the United States arm and train a cadre of opposition fighters.
With the violence escalating, Aleppo under attack by Scud missiles and members of a quarrelsome Syrian opposition challenging the value of the Rome meeting — which was supposed to be a highlight of Mr. Kerry’s trip — the State Department issued a statement on Saturday evening that condemned the rocket attacks “in the strongest possible terms” and prodded the Syrian opposition to attend the session.
The statement continued, “We look forward to meeting soon with the leadership of the legitimate representative of the Syrian people, the Syrian Opposition Coalition, to discuss how the United States and other friends of the Syrian people can do more to help the Syrian people achieve the political transition that they demand and that they deserve.”