CAIRO - The Muslim Brotherhood candidate for Egypt's presidency was cheered by supporters on Thursday when he registered to run in an election where his main rivals will be other Islamists and candidates who served under the ousted president, Hosni Mubarak. Khairat el-Shater, 61, a millionaire businessman and leading strategist in the Brotherhood, was named as its candidate last week in a policy reversal by the group that previously pledged it would not participate. The Brotherhood's broad grass-roots network, built over decades, ensures Shater is a frontrunner, although he has yet to launch his campaign. "The people want Shater for president," the group of about 2,000 supporters chanted. Some lit fireworks. "This is a historical day for Egypt. Our earlier decision not to field a candidate was for Egypt and its protection. Today, our decision to field a candidate is also for Egypt's benefit and out of a sense of responsibility" Saad Husseini, a member of the Brotherhood's party, told reporters. Shater's bid for the presidency risks splitting the Islamist vote between him, a candidate who follows the stricter Salafi interpretation of Islam and another contender with more moderate views who was expelled from the Brotherhood over his decision to run before the group changed tack on fielding a candidate. That could hand the advantage to two other main contenders: Amr Moussa, the former head of the Arab League who had also served as Mubarak's foreign minister in the 1990s, and Mubarak's last prime minister Ahmed Shafiq, who, like the ex-president, was once in charge of the air force. The door for nominations closes on Sunday with any challenges to nominees reviewed after that. The first round of voting is May 23-24, followed by a second round on June 16-17. About 1,000 people have take documents to register to run for Egypt's top job. In a poll researched in March, just before Shater was named as a candidate, Moussa was frontrunner with the Salafi candidate Hazem Salah Abu Ismail in second place, and Shafiq third. Islamists already dominated parliament. The rise of Islamists is being closely watched in the West, long wary of their influence in Egypt, the first Arab state to make peace with Israel and recipient of $1.3 billion in annual US military aid. But US and other officials have lined up to meet Brotherhood officials, including Shater.