CAIRO — The Muslim Brotherhood nominated its chief strategist and financier Khairat el-Shater on Saturday as its candidate to become Egypt’s first president since Hosni Mubarak, breaking a pledge not to seek the top office and a monopoly on power.

Mr. Shater, 62, a millionaire business tycoon, was a political prisoner until just a year ago. Because of the Brotherhood’s unrivaled grass-roots organization and popular appeal, he is now a presidential front-runner.

He is being nominated at a moment of escalating tension between the Brotherhood and Egypt’s military rulers. The Brotherhood, an Islamist group outlawed under Mr. Mubarak, already dominates the Parliament and the assembly writing a new Constitution. It is now demanding to replace the military-led cabinet and is tussling with the military council over questions like the degree of civilian oversight of the military under the new charter.

His candidacy is likely to unnerve the West and has already outraged Egyptian liberals, who wonder what other pledges of moderation the Brotherhood may abandon.

The Brotherhood’s entry into the race also turns the election into a debate over the future of the Islamist political movement that is sure to resonate in the region. Mr. Shater faces Islamist rivals to his left and right — one a more liberal former Brotherhood leader, the other an ultraconservative Salafist. Indeed, the Brotherhood may have entered the race in part because a strong showing by either rival could undercut the group’s authority as the predominant voice of Islam in Egyptian politics.

Mr. Shater is considered a conservative but a pragmatist. He has argued that Islam demands tolerance and democracy, has championed free trade and open markets and has guided the Brotherhood through its first public commitment to uphold the peace agreement with Israel.

But he also argues for an explicitly Islamic government. And while some in the group have argued that it should tolerate diverse approaches to Islamist politics from its own members, he has helped enforce the authority of the Brotherhood’s executive committee over its members, stirring allegations from liberals that it is undemocratic.

Doubts about the strength of the Brotherhood’s commitment to its promises raise particular concerns in the United States and Israel, which considered the Mubarak government’s commitment to the peace agreement a linchpin of regional stability.

An Israeli official, speaking on condition of anonymity, declined to comment specifically on Mr. Shater, but called the nomination worrisome. “Obviously this is not good news,” the official said. “The Muslim Brotherhood is no friend of Israel’s. They do not wish us well.” The official added: “The big question will be how pragmatic they will be once in power. It could go in either direction.”

In Washington, the State Department declined to comment. But many American officials who have met with Mr. Shater on visits to Cairo, including top State Department officials and Congressional delegations, have praised his moderation, business savvy and effectiveness.

At a news conference announcing the nomination, officials of the Brotherhood and its political arm insisted they were forced to offer a candidate because of the urgent needs left by more than a year of military-led transitional government. They alluded to a mounting economic crisis as well as unspecified “threats to the revolution.”

“We decided that Egypt now needs a candidate from us to bear this responsibility,” said Mohamed el-Morsi, president the Brotherhood’s Freedom and Justice Party. “We have no desire at all to monopolize power.”

Mr. Shater was not present at the news conference. Instead, the Brotherhood’s supreme guide, Mohamed Badie, read a letter from Mr. Shater resigning his post as deputy supreme guide to run for president. “Although I never thought of occupying any executive position in the state or running for it, I can’t help but comply with the decision of the group,” Mr. Shater wrote, according to Mr. Badie.

The Brotherhood, an 84-year-old religious and anticolonialist movement that became the wellspring of Islamist ideologies around the world, was outlawed but intermittently tolerated under Mr. Mubarak, and most of its senior leaders have spent time in prison.

Mr. Shater was a favorite target because of his role as a major donor and financial manager for the group, as well as an increasingly influential strategist; he spent a total of about 12 years behind bars, more than any other Brotherhood leader. He was released last year on a suspended sentence, but his conviction was not overturned, leaving him with a record that would appear to bar him from running for office. But the Brotherhood leaders said they did not expect any legal obstacles, suggesting a deal was in the works.

After the ouster of Mr. Mubarak, it was Mr. Shater who explained to the news media that the Brotherhood had pledged not to field a presidential candidate, to avoid repeating the experience of the short-lived Islamist victory in the 1991 Algerian elections, which elicited a military crackdown and the start of a decade-long civil war.

“When Islamists there reached power quickly,” Mr. Shater said then, “the military establishment turned against them.”

On Saturday some fellow Islamists criticized the Brotherhood for abandoning its pledge. Kamal El Helbawy, an ex-spokesman for the group in Europe, resigned, saying that the Brotherhood looked like “liars” and that its political mission had taken precedence over the religious one.

Abdel Rahman Ayyash, a former member who used to work closely with Mr. Shater, accused him of merely seeking political power. “For the first time since I was a Muslim Brother, I’m certain of bad intentions,” he said.

Mr. Shater was considered a hero of Brotherhood reformers. He helped chart the group’s steps into electoral democracy, both in professional associations and as the only real opposition in the Mubarak-dominated Parliament. And he led the creation of the Brotherhood’s Web sites in Arabic and English, spawning a generation of bloggers.

In prison and out, Mr. Shater served as the Brotherhood’s chief liaison for negotiations or other exchanges with the Mubarak security services, and since Mr. Mubarak’s ouster he has continued that role with the generals.

Since the ouster of Mr. Mubarak, however, many younger and reform- minded members have said they have grown disappointed with Mr. Shater. They say he has enforced an insular and hierarchical culture left over from the group’s decades underground. Mr. Shater led a push to bar Brotherhood members from dissenting from the political stands of its Freedom and Justice Party, and he led the expulsion of those who sought less conservative Islamist politics.

One of those Mr. Shater helped expel is now among the other front- runners in the presidential campaign, Abdel Moneim Aboul Fotouh, a former senior leader of the Brotherhood and a liberal reformer within the group. Mr. Aboul Fotouh was expelled for defying the Brotherhood’s decision, now reversed, not to allow any of its members to run for president. He has continued to try to rally Brotherhood members and Islamists, as well as more liberal and secular Egyptians, to his banner.

He argues that no one has a monopoly on the application of Islam to political life, so the Islamist movement should have room for liberals and leftists as well as conservatives.

The Brotherhood has now dropped the pledge that Mr. Aboul Fotouh was expelled for violating, but the group has continued to oppose his candidacy because of his insubordination, even threatening to expel members who support him.

On the other side, Mr. Shater faces competition from an ultraconservative populist, Hazem Salah Abu Ismail, who has built a national following with an old-school Islamist platform, including vigorous attacks on Israel and the West, as well as an emphasis on restoring strict Islamic law. His success would seriously discredit the Brotherhood’s efforts to portray Egypt’s Islamists as moderate and unthreatening.

But Mr. Badie, the supreme guide, warned Mr. Shater’s opponents to watch out, reminding them that Mr. Shater’s prayers in prison for the end of the Mubarak government were answered. “To all those who will slander engineer Khairat el-Shater, his prayers against those who slander him are answered — literally by the way,” Mr. Badie said.

Mayy El Sheikh contributed reporting. (Copyright 2012 The New York Times Company 04/01/12)