* Tahrir rally a show of strength for fractious opposition
* Death toll since decree rises to two
* Leftists, liberals, others want decree scrapped
* Brotherhood cancels rival protest (Adds comment by opposition politician, clashes in Delta city)
By Edmund Blair and Tamim Elyan
CAIRO, Nov 27 (Reuters) - Opponents of President Mohamed Mursi clashed with Cairo police on Tuesday as thousands of protesters around the nation stepped up pressure on the Islamist leader to scrap a decree they say threatens Egypt with a new era of autocracy.
Police fired tear gas at stone-throwing youths in streets off the capital's Tahrir Square, heart of the uprising that toppled Hosni Mubarak last year. Protesters also turned out in Alexandria, Suez, Minya and cities in the Nile Delta.
A 52-year-old protester died after inhaling teargas in Cairo, the second death since last week's decree that expanded Mursi's powers and barred court challenges to his decisions.
Tuesday's protest called by leftists, liberals and other groups deepened the worst crisis since the Muslim Brotherhood politician was elected in June, and exposed a divide between the newly empowered Islamists and their opponents.
Mursi's administration has defended his decree as an effort to speed up reforms and complete a democratic transformation. Opponents say it shows he has dictatorial instincts.
"The people want to bring down the regime," protesters in Tahrir chanted, echoing slogans used in the anti-Mubarak revolt.
Mursi's move provoked a rebellion by judges and battered confidence in an economy struggling after two years of turmoil.
Opponents have accused Mursi of behaving like a modern-day pharaoh, a jibe long levelled at Mubarak. The United States, a benefactor to Egypt's military, has expressed concern about more turbulence in a country that has a peace treaty with Israel.
"We don't want a dictatorship again. The Mubarak regime was a dictatorship. We had a revolution to have justice and freedom," 32-year-old Ahmed Husseini said in Cairo.
Some protesters have been camped out since Friday in Tahrir, and violence has flared around the country, including in a town north of Cairo where a Muslim Brotherhood youth was killed in clashes on Sunday. Hundreds have been injured.
Supporters and opponents of Mursi threw stones at each other and some hurled petrol bombs in the Delta city of el-Mahalla el-Kubra. A doctor said nine people were brought to hospital, but he expected numbers to rise to dozens.
SHOW OF STRENGTH
The protest was a show of strength by the non-Islamist opposition, whose fractious ranks have been brought together by the crisis. Well-organised Islamists have consistently beaten more secular-minded parties at the ballot box in elections held since Mubarak was ousted in February, 2011.
"The main demand is to withdraw the constitutional declaration (decree). This is the point," said Amr Moussa, former Arab League chief and presidential candidate who has joined the opposition coalition, the National Salvation Front.
Some scholars from the prestigious al-Azhar mosque and university joined Tuesday's protest, showing that Mursi and his Brotherhood have alienated some more moderate Muslims. Members of Egypt's large Christian minority also joined in.
Mursi formally quit the Brotherhood on taking office, saying he would be a president for all Egyptians, but he is still a member of its Freedom and Justice Party.
The decree issued on Thursday expanded his powers and protected his decisions from judicial review until the election of a new parliament expected in the first half of 2013.
New York-based Human Rights Watch said it gives Mursi more power than the interim military junta from which he took over.
U.N. Secretary-General Ban Ki-moon told an Austrian paper he would encourage Mursi to resolve the issue by dialogue.
Trying to ease tensions with judges outraged at the step, Mursi has assured Egypt's highest judicial authority that elements of the decree giving his decisions immunity would apply only to matters of "sovereign" importance. Although that should limit it to issues such as a declaration of war, experts said there was room for much broader interpretation.
In another step to avoid more confrontation, the Muslim Brotherhood cancelled plans for a rival mass rally in Cairo on Tuesday to support the decree. Violence has flared in the past when both sides have taken to the streets.
But there has been no retreat on other elements of the decree, including a stipulation that the Islamist-dominated body writing a new constitution be protected from legal challenge.
"The decree must be cancelled and the constituent assembly should be reformed. All intellectuals have left it and now it is controlled by Islamists," said 50-year-old Noha Abol Fotouh.
With its popular legitimacy undermined by the withdrawal of most of its non-Islamist members, the assembly faces a series of court cases from plaintiffs who claim it was formed illegally.
Mursi issued the decree on Nov. 22, a day after he won U.S. and international praise for brokering an end to eight days of violence between Israel and Hamas around the Gaza Strip.
Mursi's decree was seen as targeting in part a legal establishment still largely unreformed from Mubarak's era, when the Brotherhood was outlawed.
Though both Islamists and their opponents broadly agree that the judiciary needs reform, Mursi's rivals oppose his methods.
Rulings from an array of courts this year have dealt a series of blows to the Brotherhood, leading to the dissolution of the first constitutional assembly and the lower house of parliament elected a year ago. The Brotherhood dominated both.
The judiciary blocked an attempt by Mursi to reconvene the Brotherhood-led parliament after his election victory. It also stood in the way of his attempt to sack the prosecutor general, another Mubarak holdover, in October.
In his decree, Mursi gave himself the power to sack that prosecutor and appoint a new one. In open defiance of Mursi, some judges are refusing to acknowledge that step.
Mursi has repeatedly stated the decree will stay only until a new parliament is elected - something that can happen once the constitution is written and passed in a popular referendum. (Additional reporting by Tom Perry, Seham Eloraby, Marwa Awad and Yasmine Saleh in Cairo and Michael Shields in Vienna; Writing by Edmund Blair and Tom Perry; Editing by Anna Willard, David Stamp and Alastair Macdonald)