* Sisi says cannot perform miracles, Egypt faces "great challenges"
* Student killed in clashes with police at Cairo University
* U.S. urges "free, fair" elections
* Clashes follow death sentences for Brotherhood members
* Prosecutor orders 919 more Brotherhood members to stand trial (Adds U.S. reaction)
By Tom Perry and Mahmoud Mourad
CAIRO, March 26 (Reuters) - Abdel Fattah al-Sisi, the general who ousted Egypt's first freely elected leader, declared his candidacy on Wednesday for a presidential election he is expected to easily win.
Sisi toppled Mohamed Mursi of the Muslim Brotherhood last July after mass protests against his rule and has emerged as the most influential figure in an interim administration that has governed since then.
"I am here before you humbly stating my intention to run for the presidency of the Arab Republic of Egypt," Sisi said in a televised address to the nation. "Only your support will grant me this great honour."
A Sisi presidency would mark a return to the days when Egypt was led by men from the military, a pattern briefly interrupted by Mursi's one year in office after his 2012 victory in Egypt's first democratic presidential election.
Among his supporters, Sisi is wildly popular. Many see him as the kind of strong man needed to stabilize a country in crisis. But he is reviled by the Islamist opposition as the mastermind of a coup against a freely elected leader.
Dressed in military fatigues, Sisi vowed to fight what he described as a terrorist threat facing Egypt, a reference to militant attacks that have spiralled since he ousted Mursi.
"True, today is my last day in military uniform, but I will continue to fight every day for an Egypt free of fear and terrorism," said Sisi, 59, who had to resign his posts of army chief and minister of defence so he could run in the election.
General Sedki Sobhi, formally chief of staff, replaces Sisi as head of the army.
Seeking to cap sky-high expectations, Sisi warned he could not perform "miracles" in a country of 85 million that is steeped in poverty. "I cannot make miracles. Rather, I propose hard work and self-denial," he said.
Before his address, state TV broadcast montages including footage of Sisi jogging with troops. He has been lionized by privately owned and state media that are hostile to the Islamists.
He said, "We must be truthful with ourselves. Our country faces great challenges. Our economy is weak. There are millions of youths who suffer from unemployment in Egypt."
Leftist politician Hamdeen Sabahi is the only other declared candidate for the election. He came in third in the 2012 election.
Commenting on Sisi's candidacy, the United States, a major source of military aid to Egypt, said it did not support individual candidates or parties in Egyptian elections.
"As the election process moves forward we urge the Egyptian authorities to ensure that the elections are free, fair, and transparent; that all candidates are able to campaign freely, without fear of harassment or intimidation; and that the views of all the Egyptian people are fully represented," White House National Security Council spokeswoman Bernadette Meehan said in a statement.
DEATH IN CAIRO
Sisi would assume leadership of a country that has faced unending turmoil since the uprising that toppled Hosni Mubarak in 2011. Since the army toppled Mursi, Egypt has suffered the worst internal strife in its modern history.
The security forces killed hundreds of his supporters after his removal from power, and police and soldiers have become the main targets in a campaign of bombings and shootings.
There were reminders of the instability on Wednesday, when one student was killed in protests at Cairo University that were ignited by a court's decision on Monday to sentence 529 members of the Muslim Brotherhood to death.
Almost the entire leadership of the Brotherhood is in jail. Mursi faces charges that could lead to the death penalty.
The public prosecutor on Wednesday ordered 919 Brotherhood members to stand trial on charges including murder and terrorism in the southern province of Minya, the same province where Monday's verdicts were handed down.
"If (Sisi) doesn't have a real plan for reconciliation, he certainly will fail. But I don't know if he will be able to do it," said Hassan Nafaa, a professor of political science at Cairo University.
Monday's court ruling drew criticism from international human rights groups and Western powers.
Washington expressed fresh criticism of Cairo, with Secretary of State John Kerry saying he was "deeply, deeply troubled by the sudden and unprecedented decision" by the Egyptian court to issue death sentences for 529 defendants "after a quick mass trial."
"I urge the interim Egyptian government to reverse the court ruling and ensure due process for the accused. Anything less would dishonour the bravery of all who sacrificed their lives for democratic values," Kerry said, referring to the earlier Egyptian street protests.
Kerry said it was impossible to believe the court proceedings "satisfied even the most basic standards of justice."
Kerry said on March 12 that he would decide "in the days ahead" whether to resume American aid to Egypt after suspending the funds last year over the ouster of Mursi.
European Council President Herman van Rompuy said after meeting U.S. President Barack Obama that the United States and the European Union were "appalled" by the sentences.
"We urge the Egyptian authorities to restore the rule of law," he told a news conference. (Reporting by Tom Perry and Mahmoud Mourad; Additional reporting by Will Dunham in Washington and Justyna Pawlak and Steve Holland in Brussels; Editing by Michael Georgy, Robin Pomeroy, Lisa Shumaker, Peter Cooney, Toni Reinhold)