Five hundred days after they overthrew Hosni Mubarak, Egyptians are about to gain a new president. This marks the first time they have chosen freely, and the winner may well be the candidate from the Muslim Brotherhood, an organization which Mubarak and fellow generals spent a lifetime fighting.

The result of last weekend's run-off, due for release in an election committee news conference at 3 p.m. (Israel time), will be historic for Egypt and the Middle East. Many think Islamist Mohammed Morsi will become head of state in the largest Arab nation, reshaping the region after decades of Western-backed military rule, even if the armed forces are not giving up their control just yet.

The brotherhood may react angrily if the new president is, instead, Ahmed Shafiq, a former air force commander and Mubarak ally. Many Egyptians, and millions across the region, fear his victory would be a mortal blow to last year's Arab Spring revolution, despite his assurances of also wanting an inclusive government.

On Saturday, a bloc of liberal and leftist parties represented in the disbanded parliament— the Free Egyptians, the Tagammu, and the National Democratic Front — held a news conference accusing the brotherhood of trying to blackmail elections officials with street demonstrations.

The liberal parties accused the U.S. of pressuring the ruling military council to hand power over to the brotherhood.

"We have seen the U.S. forcing the military council to hand power to the brotherhood," said Osama el-Ghazali Harb of the Democratic Front.

Activist Mahmoud al-Allali said U.S. Secretary of State Hillary Rodham Clinton, "is giving directions and instructions, directly and sharply."

On Wednesday, Clinton had demanded that the military, "support the democratic transition, to recede by turning over authority."

Clinton criticized the military's attempts to keep a strong grip on power and said, "The military has to assume an appropriate role, which is not to try to interfere with, dominate or subvert the constitutional authority."

U.S. officials had earlier expressed concern that a Shafiq victory could have dangerous fallout, with protests and ensuing instability that might lead the military to take even stronger measures. The officials spoke on condition of anonymity due to the sensitivity of the matter.

After an anxious week of street protests at Cairo's Tahrir Square and angry accusations by rivals accusing each other of subverting the new democracy, the new president will emerge with less power than the candidates expected when the army committed itself to civilian rule beginning July 1.

The ruling military council, which pushed Mubarak aside to appease the protesters in the streets, recently stripped the post of many powers and dissolved the brotherhood-dominated parliament elected in January. Yet the presidency is still a prize, even if the vote will not end the power struggles over Egypt's future.

An Islamist president of Egypt would be a major milestone for the Middle East, nearly unthinkable 18 months ago. It is far from confirmed, but the military, the brotherhood and other officials gave signs of expecting it to happen.

Brotherhood supporters camped out in Tahrir Square, where the revolution developed, were generally in a festive mood, though fear of disappointment still nagged after decades of rigged elections. To counter this, a few thousand people rallied on Saturday in a middle-class Cairo suburb to declare support for the army.

Morsi, a 60-year-old, U.S.-educated engineer and political prisoner under Mubarak, declared victory within hours of polls closing last Sunday, a move condemned by military generals. In a sign of continued confidence, he has already met other groups and drafted an accord to form a national coalition government.

His party issued a statement on Saturday saying it had called on "all partners in the nation, from all movements, to take part in this national platform, to guarantee the success of what we have achieved and their active participation in rebuilding the country in the manner it deserves.”

One of those involved, Abdel Gelil Mostafa of the reformist National Association for Change, told Reuters on Saturday: "We agreed on a general program, especially for if Morsi won. That seems probable. But we will know tomorrow."

In contrast, supporters of Shafiq, 70, who was Mubarak's last prime minister, kept a low profile, although he did declare publicly on Thursday he was confident.

A victory for Shafiq, who won backing in the run-off from many who decided they liked religious rule even less than a candidate drawn from the familiar military establishment, could spark protests from well-organized Islamist movements, which the army and security forces might confront in the streets.

Reformist politician Mohamed ElBaradei said he had been in contact with the army and Morsi's camp to avoid a showdown, but expressed fears that, if Shafiq were declared winner, "we are in for a lot of instability and violence ... a major uprising." His comments were carried by CNN on Saturday.

There have been indications from senior figures in the brotherhood and military council that they have held meetings to prepare for a Morsi presidency since the election.

While officials deny any negotiation over the drawn-out process of tallying the election results themselves, if Morsi is made head of state.

there would be greater scope for compromise to defuse tension over what many have called the army's "soft coup" against parliament and the powers of the president.

The brotherhood has said it will go on protesting until the military council revokes its dissolution of parliament and its decree which granted legislative powers to itself, the Supreme Council of the Armed Forces. Were its candidate to be confirmed in office, the wary symbiosis formed between the two enemies since Mubarak was ousted may continue in a new form.

It is a collaboration that irks many of the secular liberals who led the first wave of the uprising against Mubarak but found themselves fragmented and eliminated in last month's first round of voting, left with a difficult choice between the army and Islam.

Thousands of brotherhood supporters were in Tahrir Square again on Saturday, chanting "Victory for Morsi!" and "Morsi, Morsi, Allahu akbar!" (“God is great”), while waving national flags.

"We want the military council to announce the real results without forgery," said Hassan Eissa, 43, an accountant from north of Cairo who was demonstrating on the square. "They have no right [to rule]. Egyptians shouldn't be under any kind of guardianship after the revolution."

The generals, who oversaw Mubarak's departure on Feb. 11, 2011, have repeatedly said, both to Egyptians and to their close ally, the U.S., that they will return to their barracks to make way for civilian rule. But they present themselves as guardians of Egypt's security and long-term interests and have moved to block the Islamists from taking more than a share of power.

While they have said that inaugurating the new president by July 1 will meet the deadline they set for civilian rule, their moves in the past 10 days to curb the presidency and retain a veto over legislation, as well as to claim a role in drafting a new constitution, mean that the process goes on.

The U.S. and the EU, both major aid donors to Egypt, have expressed concern that the military is backtracking. But both also share its anxiety over a sweeping Islamist takeover, worried about Egypt turning anti-Western and reneging on its peace with Israel, and also voicing concern for civil rights.

Violence by hardline Islamists in Tunisia, whose revolt inspired that in Egypt, has troubled many Egyptian liberals.

Drafting a constitution is the key to the transition to democracy. That work has been hostage to partisan wrangling in the now defunct parliament, where one assembly collapsed after complaints it was too Islamist and a second faces a challenge in court on Tuesday that many expect to trigger a clause in the military council decree letting it name a new drafting panel.

The brotherhood has portrayed itself as a modern movement, ready to work with others and willing to respect treaties. Some supporters cite the example of Turkey as a model — a Muslim democracy with a history of military interference in politics, where devout, elected politicians have slowly asserted control.

The bearded, bespectacled Morsi was not a familiar figure to Egyptians. Some ridicule him as the movement's "spare tire"; his campaign began after a more senior leader was barred from the race. Critics say he would be a mere frontman as president, for less visible pillars of the brotherhood behind the scenes.

Meanwhile, former Egyptian Foreign Minister Amr Moussa met with MK Isaac Herzog (Labor) on Saturday in Brussels during an EU conference on challenges in the Middle East.

During the conference, Moussa said, "The peace treaty with Israel has to be revisited and modified, but it must be preserved."

His comments run counter to those made by Muslim Brotherhood officials, who have called for annulling the peace treaty.

In January, Essam Arian, deputy head of the Muslim Brotherhood's Freedom and Justice Party, said, "We never promised that we would honor the peace treaty with Israel. The treaty is not sacred and we can and should make changes in it."

Another senior member of the party told the London-based newspaper Asharq Alawsat, "The movement's position is not to recognize the Zionist entity and not to recognize peace agreements with hostile entities, and this position will never change."