Pakistan banned protests in two provinces and arrested scores of lawyers and opposition leaders Wednesday ahead of planned rallies threatening to batter the already-shaky rule of its pro-Western government.

The crackdown by police and intelligence agencies will damage the democratic credentials of the ruling party of President Asif Ali Zardari and will surely stoke further anger at his six-month rule. Lawyers vowed to continue their protests regardless.

The political crisis comes as the nuclear-armed country is grappling to contain surging violence by al-Qaida and the Taliban and fix an economy that remains functioning only because of support from international lenders. It could lead to a political meltdown and even some form of intervention by the country's powerful military, which has often seized power in the past following chaotic civilian rule.

The turmoil erupted last month when the Supreme Court banned the head of the largest opposition party, Nawaz Sharif, and his brother, from elected office. They accused Zardari of engineering the verdict to neutralize them.

They and other opposition parties are now supporting lawyers' demands that Zardari fulfill a pledge to restore judges fired by former President Pervez Musharraf and create an independent judiciary. The justices are believed likely to be hostile to Zardari and could move to limit his powers.

The protesters have vowed to gather in cities around the country Thursday before leaving for the capital, Islamabad, where they plan to stage a sit-in at the parliament building until their demands are met.

In a move seemingly designed to thwart that protest, Rao Iftikhar, the home secretary in eastern Punjab province, said he issued orders for a ban on public gatherings there "so that terrorists cannot take any advantage by targeting political gatherings." The ban will remain in force for three months, he said. It gives authorities the right to arrest any protesters.

Punjab is Pakistan's most powerful and populous province and Sharif's political stronghold.

Sindh province Home Secretary Arif Ahmad Khan also announced a 15-day ban on public gatherings, ostensibly to "prevent a bad law and order situation." Sindh is the main stronghold of the ruling Pakistan People's Party.

A spokesman for Sharif's party, Sadiqul Farooq, said he received reports from party offices across the country that members were being arrested, but he had no accurate numbers. Munawar Hassan, a leader of the Islamist Jamaat-e-Islami Pakistan party, said "nearly two dozen of our supporters have been detained."

Farhatullah Babar, a spokesman for Zardari, said 18 people had been arrested and would be released once the situation calmed down.

"Some people have announced they are going to defy the ban on public meetings," he said. "It is sad, but this is what the law says."

In the Punjabi city of Multan, senior police officer Fayyaz Ahmad said 42 Sharif supporters were arrested and "would be dealt with according to the law."

On Monday, the country's security chief said the protesters were welcome to rally, but urged them not to gather in front of the parliament. He suggested they protest in an empty lot on the outskirts of Islamabad. The protesters insist they are planning a peaceful march.

Aitzaz Ahsan, a protest leader, said he believed "hundreds" of lawyers had been arrested, but insisted the movement -- which helped bring down the government of Musharraf -- would not falter.

"How long can the state resist?" he told a local TV station. "We will keep on knocking on the door of Islamabad relentlessly."

Zardari is the widower of slain former Prime Minister Benazir Bhutto, who was widely praised as a democrat. He has repeatedly promised to implement her vision in the country of 170 million people.

Bhutto's and Sharif's parties were bitter rivals in the 1990s, a turbulent decade when both leaders served twice as prime minister without completing a term before Musharraf seized power.