America yesterday swung its support behind Egypt's vice-president, Omar Suleiman, and the political transition he is leading, calling for a process of orderly reform. The policy, made clear by Hillary Clinton at the Munich Security Conference, was the latest sign of steps by the US and senior members of the Egyptian military to nudge President Hosni Mubarak aside and contain the potential for street violence.

The move came as senior members of the leadership of the ruling National Democratic party resigned from the party in response to the protests. They included Mubarak's powerful son, Gamal, long expected to succeed his father. A relative liberal, Hossam Badrawi, was appointed the party's new secretary general.

The mass resignation, announced yesterday afternoon, is likely to be seen as a further sign of Mubarak's weakness and will only strengthen the demands of protesters determined to topple him. It appeared to be part of a strategy agreed with the US to manage the transition, with or without Mubarak, as power shifts to Egypt's vice-president, who is backed by the Americans to head the political transition.

"There are forces in any society, particularly one facing these kind of challenges, that will try to derail or overtake the process to pursue their own agenda, which is why I think it's important to follow the transition process announced by the Egyptian government, actually headed by vice-president Omar Suleiman," Clinton told western politicians, diplomats and business leaders at the annual conference.

She added that the transition should be transparent and inclusive, and the process should set out "concrete steps" towards orderly elections in September. David Cameron and the German chancellor, Angela Merkel,, speaking at the same conference, echoed the call for an orderly transition and cautioned against early elections.

Frank Wisner, the White House envoy sent to Cairo last Monday to press Mubarak to agree to democratic reforms, said yesterday that he believed the president should remain in office through the transition period.

"You need to get a national consensus around the preconditions of the next step forward, and the president must stay in office to steer those changes through," he told the conference. "I therefore believe that President Mubarak's continued leadership is critical; it's his opportunity to write his own legacy." Last night the US state department appeared to distance itself from Wisner's remarks, claiming that the comments were "his own".

US backing for Suleiman and its failure to press for Mubarak's immediate resignation will dismay many anti-government protesters who have failed to force the president out despite mass demonstrations across the country on Friday. Some protesters are suspicious of the American backing for Suleiman overseeing the political transition because of his role as Mubarak's intelligence chief.

"We won't accept this American plan if it does not cut off the head of the snake," said Ahmed Mora, a university lecturer among the demonstrators. "America has not been good for us in Egypt. It supported Mubarak for 30 years. If he's still there, or other people from the system are still there, we will not accept it."

Anti-Mubarak protesters have called for another mass rally in Tahrir Square today after Friday's protest. Yesterday the mood was calm, but many demonstrators said that Mubarak's evident weakness had only reinforced their determination to continue the campaign. His resignation from the party leadership came after he said he would not run for president at the next election, scheduled for September. Mubarak said he would remain in office until then.

Clinton's and Cameron's statements may be crucial in allowing him to stand down according to his own timetable in the summer. Cameron denied there was a trade-off between the speed of reform and stability: "There is no stability in Egypt. We need change, reform and transition to get stability. The longer that is put off, the more likely we are to get an Egypt that we wouldn't welcome."

British officials said they were encouraged by the developments of the past 24 hours, pointing to the role of the army in preventing attacks on the demonstrators and the opening of a dialogue between Suleiman and opposition groups.

Clinton listed with approval the steps the Egyptian government had taken so far. "President Mubarak has announced he will not stand for re-election, nor will his son. He has given a clear message to his government to lead and support this process of transition," she said."That is what the government has said it is trying to do, that is what we are supporting, and hope to see it move as orderly but as expeditiously as possible under the circumstances."