WRAPUP 3-Egypt's bruised Brotherhood seeks to shows street power
* Troops, police stand by to foil Brotherhood marches
* Islamist movement reeling from bloodshed, arrests
* Trial of its top three leaders to open on Sunday
CAIRO, Aug 23 (Reuters) - Egyptian troops and police stood ready in Cairo to foil Muslim Brotherhood plans for "Friday of Martyrs" protests against the army's bloody crackdown on followers of ousted President Mohamed Mursi.
The Brotherhood, hounded by Egypt's new army-backed rulers, has called for marches from 28 mosques after midday prayers in Cairo, testing the resilience of its battered support base.
Security precautions appeared relatively low-key, even near the Fateh mosque in the heart of the capital where gun battles raged last Friday and Saturday, killing scores of people.
The mosque's metal gates and big front door were locked and chained. A doorman said prayers had been cancelled. Two armoured personnel carriers were parked down the street, where people shopped at a bustling market.
Egypt has endured the bloodiest civil unrest in its modern history since Aug. 14 when police destroyed protest camps set up by Mursi's supporters in Cairo to demand the reinstatement of the Islamist president, who was deposed by the army on July 3 after huge demonstrations against his first year's rule.
Only one riot police truck was parked near the Rabaa al-Adawiya square in northeastern Cairo, home to the Brotherhood's biggest protest vigil until police and troops stormed in, killing hundreds of people, bulldozing barricades and burning tents.
The mosque there was closed for repairs. Workmen in blue overalls stood on scaffolding as they covered its charred walls with white paint. Children scavenged through piles of garbage.
Troops used barbed wire to block off a thoroughfare leading to Nahda Square, the site of the smaller of the two Brotherhood sit-ins.
Traffic moved freely around the huge Nour mosque in the Abbaseya neighbourhood. There were no armoured vehicles or barbed wire, but Friday prayers there had also been cancelled.
The authorities declared a month-long state of emergency last week and they enforce a nightly curfew. The state news agency said the armed forces had strengthened their presence around the presidential palace and the defence ministry.
The Muslim Brotherhood, which won five successive votes held in Egypt after the overthrow of Hosni Mubarak in 2011, is reeling from a week of bloodshed and the arrest of many of its leaders in what the authorities call a battle with terrorism.
In a symbolic victory for the army-dominated old order, Hosni Mubarak, the ex-military former president who ruled Egypt with an iron fist for 30 years before a popular uprising toppled him in 2011, was freed from jail on Thursday. His successor Mursi, Egypt's first freely elected president, remains behind bars.
The Brotherhood's "General Guide" Mohamed Badie, who was arrested on Tuesday, is due to go on trial on Sunday along with his two deputies, Khairat al-Shater and Saad al-Katatni, on charges that include incitement to violence.
At least 900 people, including about 100 soldiers and police, have been killed in violence across Egypt since Aug. 14, officials say. Brotherhood supporters say the toll is higher.
The Brotherhood, founded in 1928, could once mobilise vast crowds, drawing on the same organisational strength it wielded at the ballot box, but its protests have dwindled this week in the face of the security crackdown.
"We will remain steadfast on the road to defeating the military coup," the pro-Mursi National Coalition to Support Legitimacy and Reject the Coup said in a statement.
Graffiti on a mosque wall in central Cairo illustrated the deep divisions that have emerged since army chief Abdel Fattah al-Sisi ousted Mursi.
The spraypainted message "yes to Sisi" had been crossed out and painted over with the word "traitor." Slogans elsewhere read "Mursi is a spy" and "Mursi out". Someone had also written "Freedom, Justice, Brotherhood."
The Brotherhood survived for generations as an underground movement before emerging as Egypt's best-drilled political force after Mubarak fell. But its popularity waned during Mursi's year in office when critics accused it of accumulating power, pushing an Islamist agenda and mismanaging the economy.
The Brotherhood, which Egypt's new army-backed rulers have threatened to dissolve, says Mursi's government was deliberately undermined by unreconstructed Mubarak-era institutions.
Mubarak, 85, still faces retrial on charges of complicity in the killings of protesters, but he left jail on Thursday for the first time since April 2011 and was flown by helicopter to a plush military hospital in the southern Cairo suburb of Maadi.
The authorities have used the state of emergency to keep him under house arrest, apparently to minimise the risk of popular anger if he had been given unfettered freedom. Local newspapers on Friday focused on the latest arrest of Brotherhood leaders, giving scant coverage to the former strongman's exit from jail.
"Mubarak will never be an important political player, but symbolically it's a victory dance by the reconstituted old state," Joshua Stacher, an Egypt expert at Kent State University in the United States, said of the former leader's release.
Adding to a sense among some activists that the freedoms won in the 2011 revolt are in danger, planned amendments to the constitution leaked to the media this week appear designed to place limits on political parties and ease restrictions on the participation of Mubarak-era officials in politics.
(Additional reporting by Cairo bureau; Writing by Alistair Lyon; Editing by Will Waterman)