CAIRO — The runoff to become Egypt’s first freely elected president is shaping up as a contest between two of the most powerful and polarizing forces in Egyptian society: political Islam or the leadership of the past.

After a wild and fluid two-month campaign by more than a dozen candidates, Mohamed Morsi of the Muslim Brotherhood and Ahmed Shafik, a former air force general who served as President Hosni Mubarak’s final prime minister, emerged with the most votes on Friday, according to independent tallies and the official state news media.

Mr. Morsi won about a quarter of the vote and Mr. Shafik slightly less, effectively reprising the power struggle decades old between a military-backed, secular strongman and Islamists from the Muslim Brotherhood. At least for the moment, the results appeared to dim the hope that last year’s popular uprising would open a middle path, transcending divisions that kept Egypt paralyzed between fear of religious radicalism and fear of the secular police state.

The outcome provoked frantic warnings on Friday of either a counterrevolution should Mr. Shafik win, or an Islamist takeover, should Mr. Morsi emerge as the next president. The candidates who tried to offer a more unifying vision — and were critical of both the Mubarak era and the Brotherhood — failed to overcome the deep divisions in Egyptian society.

The result will be a runoff that offers a wrenching choice for the majority of voters who cast their ballots for one of the other candidates.

“It is a shock,” said Ahmed Kabany, 38, an engineer, after the voting. “I don’t want either one, so I am not going to vote.”

Although Mr. Shafik never explicitly promised to resurrect the old order, he campaigned as a strongman who would crack down on street protests, restore law and order and check the power of the Islamists. He surged in popularity toward the end of the campaign, by playing to voters’ fears of crime and lawlessness, and to the worries of Egypt’s Christian minority about the growing power of the Islamists, who already control Parliament.

And he never backed away from comments he made during the uprising against Mr. Mubarak comparing the insurrection to a disrespectful child who slaps his father.

Mr. Morsi, facing a serious challenge from an Islamist rival during the campaign, reverted to a conservative and expressly religious appeal, portraying his platform as a distillation of Islam itself while promising to carry out Islamic law.

Although both candidates have pledged to support the peace treaty with Israel, the runoff set up a stark choice between the Brotherhood’s vows to unite Palestinian factions in order to increase pressure on Israel to recognize a Palestinian state and Mr. Shafik’s pledges of continuity with positions of the former government.

Though official final results are to be released in a few days, early returns show that about 20 percent voted for Abdel Moneim Aboul Fotouh, a former Brotherhood leader campaigning as both an Islamist and as a liberal in an effort to break out of Egypt’s culture war. And another roughly 20 percent voted for Hamdeen Sabahi, a secular populist with a record of fighting the Mubarak government on behalf of the poor. (Fifth place went to Amr Moussa, a former foreign minister who presented a softer and more conciliatory version of Mr. Shafik’s secular law-and-order appeal.)

Handicapping the runoff was all but impossible. Although candidates from the Muslim Brotherhood or more conservative Islamist parties won about three-quarters of the seats in Parliament, Islamists and more secular candidates split the vote in the first stage of the presidential election. It was unclear whether voters who picked Mr. Sabahi, the secular populist, would lean toward Mr. Morsi to avoid returning a Mubarak minister to power, or to Mr. Shafik in order to avoid giving so much power to the Brotherhood. But at the end of the day, the possibility of low turnout favors the Brotherhood because its vast political machine can drive its voters to the polls.

As soon as the results became clear, each of the two leading candidates began to try to shift to the center, by rallying against the other. In a Friday night news conference, officials of the Muslim Brotherhood announced that they were inviting the other “revolutionary candidates” — effectively, all but Mr. Shafik — to a meeting to talk about a coalition to oppose the former prime minister and about sharing power in a Brotherhood-led government.

“Rescuing the homeland includes securing victory for a candidate who belongs to the revolutionary camp, and the camp that struggles against the old regime,” Essam el-Erian, a Brotherhood lawmaker, said, trying to portray Mr. Morsi as the champion of the whole popular uprising and not just the Islamist forces.

Supporters of Mr. Shafik, meanwhile, circulated a cellphone message urging unity against the Brotherhood. “I beg you to please put your differences aside and go vote for Shafik not because you believe in him but because it will be a catastrophe if we consolidate all power to one party (presidency and Parliament)!” the message read. “History has proved, so please spread!”

The race is further complicated by the uncertainty about the powers of the next president. A committee picked by Parliament that was supposed to draft a new charter has become deadlocked in a dispute between Islamists and liberals. The military council that has governed Egypt since Mr. Mubarak’s ouster says it will issue an interim constitution to define the president’s powers, but it has not yet done so.

Mr. Shafik has close ties to the members of the military council, and his opponents often accuse the generals of actively supporting his campaign, but no conclusive evidence has emerged. Indeed, the Brotherhood has also indicated that it intends to take a conciliatory approach toward the generals, allowing them to preserve the commercial empire they control, protecting their budget from public scrutiny and keeping them out of civilian courts.

Mr. Morsi, the least charismatic of the leading candidates in the race, relied mainly on the Brotherhood’s political machine to turn out his voters. He sat out the one televised debate, and his face barely appeared in his television commercials.

Mr. Shafik, a gruff former fighter pilot, earned the nickname “the Pullover” for the sweaters he wore in television interviews and on campaign posters, apparently to make him seem more approachable. It was all but unheard-of for a Mubarak minister to appear in public without a jacket and tie.

Both Mr. Morsi and Mr. Shafik were derided for their awkward speaking styles. During his brief tenure as prime minister, Mr. Shafik was forced to resign after a humiliating public debate on a television talk show with a liberal critic and author, Alaa al-Aswany. “I fought in wars,” Mr. Shafik said in exasperation at one point. “I killed and was killed.”

His signature campaign commercial plays to the public anxieties about the crime and lawlessness that have swept Egypt since Mr. Mubarak’s ouster, when police and security forces scattered or stopped working. The commercial begins with jarring television images of protests and riots, and the clipped voice of a television newscaster in the background.

“Chaos,” the voice says. “The country has fallen.” Then, over somber notes from a piano, Mr. Shafik says, “Egypts needs justice, and the safety for its citizens.” (Copyright 2012 The New York Times Company 05/26/12)