LAHORE, Pakistan (Reuters) - Pakistani opposition leader Benazir Bhutto called on Tuesday for military leader Pervez Musharraf to step down as president, isolating him in the run-up to a general election.

Britain stepped up international pressure on Musharraf, who imposed emergency rule on November 3, backing a 10-day Commonwealth ultimatum for him to end the emergency and quit as army chief.

Bhutto has long called for Musharraf to step down as army chief and become a civilian president but it was the first time she had called for him to quit as president altogether. She also said she could never serve as prime minister under him.

"It is time for him to go. He must quit as president," Bhutto, who has for months held power-sharing negotiations with Musharraf, told Reuters in a telephone interview.

She was speaking from the city of Lahore where she was placed under house arrest hours before a planned protest against emergency rule.

Musharraf set off a storm of criticism when he imposed the emergency, suspended the constitution, sacked most judges, locked up lawyers, rounded up thousands of opposition and rights activists and curbed the media.
The crisis in nuclear-armed Pakistan has raised fears about its stability and its ability to focus on battling a growing Islamist militancy.

"CONTAMINATED"

"I will not serve as prime minister as long as Musharraf is president," Bhutto said. "Even if I wanted to work with him, I would not have the public support."

"Negotiations between us have broken down over the massive use of police force against women and children. There's no question now of getting this back on track because anyone who is associated with General Musharraf gets contaminated," she said.

"The men whose wives have been mistreated, the women who have seen their spouses thrashed and beaten up in front of their eyes don't want us to have anything to do with General Musharraf."

Bhutto said Musharraf appeared "out of his depth": "There's a huge crisis."

A spokesman for Musharraf, who took power in a 1999 coup, declined to comment.

Two-time prime minister Bhutto planned to lead a motorcade on a 270 km (170 mile) route from Lahore to Islamabad to demand that Musharraf quit as army chief, end emergency rule, reinstate the constitution and free detained activists -- including the 7,500 Bhutto said were from her party.

Lahore is Pakistan's political nerve centre, the capital of Punjab province which is ruled by Musharraf supporters who are expected to suffer heavy losses in a general election the president has promised will be held before January 9.

But about 4,000 police moved in overnight around the Lahore house where Bhutto is staying, laying out coils of barbed wire, setting up barricades and blocking streets with trucks laden with sand. Police in riot vests and carrying batons manned barricades set up around a 1-km (half-mile) perimeter.

A detention order was pasted on the gate.

"Her residence is an official jail now," said a senior officer outside the house.

Police detained dozens of men and women chanting "Go Musharraf go" as they tried to pull down a barbed wire barricade. A Bhutto aide, Farzana Raja, was held after she tried to push her way past police to get to the house.

PRESSURE

Musharraf has come under growing pressure from Western allies to set Pakistan back on the path to democracy. He has declined to say when the constitution would be restored and said the emergency would ensure a fair vote.
Bhutto, dogged by accusations of corruption during her rule, said her party, Pakistan's biggest, might boycott the polls: "We haven't taken a final decision but that is the inclination.

U.N. Secretary General Ban Ki-moon and U.S. President George W. Bush both urged Musharraf on Monday to lift the emergency.

The Commonwealth gave him until November 22 to end emergency rule, restore the constitution and quit the army or face suspension.

British Foreign Secretary David Miliband, asked if the British government backed that call, said: "Absolutely, the Commonwealth position was one that the UK played an important part in creating."

Musharraf has justified the emergency by saying a meddling judiciary was hampering the battle against militants.
Diplomats say his main objective was to stop the Supreme Court from ruling invalid his October 6 re-election by legislative assemblies dominated by his supporters.

Musharraf has said he would step down as army chief and be sworn in as a civilian president as soon as the Supreme Court, where new judges seen as friendly to the government have been appointed, ruled on challenges to his election.