Riot police arrested dozens of opposition activists protesting against President Gen. Pervez Musharraf on Monday as Pakistan's Supreme Court dismissed two three challenges to his re-election bid.

However, the court was still weighing seven other petitions arguing that Musharraf's dual role as army chief and president is illegal and that he is ineligible to seek another five-year term.

Opposition parties said hundreds of their members have been arrested after police began taking their leaders into preventive custody late Saturday for allegedly planning to foment unrest. Officials imposed a ban on gatherings of more than five people in the capital.

Ahsan Iqbal, spokesman for the party of exiled former Prime Minister Nawaz Sharif, said more than 150 party workers have been arrested in raids across Punjab province.

"The government is bent upon picking up every opposition man," Iqbal said. "All fascist tactics are being used and all the state machinery is being exploited for the illegitimate rule of one man."

The ruling Pakistan Muslim League-Q party nominated Musharraf for the presidency after he offered last week to quit as army chief if he wins another term as head of state.

Opposition parties claim Musharraf cannot legally run for office while still in uniform, and on Friday, an opposition alliance vowed that its legislators would resign from the assemblies on Sept. 29 to deny the presidential vote legitimacy. A presidential vote by federal and provincial legislators is now scheduled for Oct. 6.

Presiding Judge Rana Bhagwandas dismissed, without explanation, two of the petitions against Musharraf's bid.

The first was filed by a retired government official arguing that Musharraf should step down immediately as president. The judge also rejected a complaint that the courts had failed to stop a constitutional amendment in 2003 that allowed Musharraf to serve as both president and head of the military. Bhagwandas said it was too late to address that grievance.

A third petition was dismissed because the lawyer who had filed it failed to appear.

The court is expected to rule later this week on the other petitions, which include complaints from opposition parties and a lawyers organization.

Also Monday, Pakistan's legal fraternity named the first candidate to challenge Musharraf in the vote by federal and provincial legislators.

"We have nominated well-respected Justice Wajihuddin Ahmed as our presidential candidate," Munir Malik, President Supreme Court Bar Association, told The Associated Press. He is expected to file his nomination papers Thursday, the same day Musharraf plans to do so.

Ahmed is not seen as a legitimate contender, but his candidacy can be used to mount further legal challenges.

Roads leading to the court were blocked with barbed wire. TV footage showed some would-be protesters sprinting away as riot police approached, but dozens began regrouping later, punching their fists in the air as they chanted slogans against the president.

Police arrested about 30 who congregated a few hundred yards from the court shouting anti-Musharraf slogans. "The U.S. government hired a dog in uniform," protesters shouted, referring to Musharraf's alliance with Washington.

Detainees were bundled into police vehicles. Others were chased off by police down the road, away from the court.

The government threw a chill into the opposition movement with the crackdown. In addition to the leaders arrested in police sweeps Saturday night in Islamabad, others who were targeted went into hiding, calling the detentions a sign of desperation by the president.

"The government has ordered the arrests of opposition leaders because they were threatening (to create) a law and order problem in the capital," Deputy Information Minister Sen. Tariq Azim told The Associated Press on Sunday, confirming the detention of "five or six" senior figures in the opposition coalition, the All Parties Democratic Movement.

"Nobody will be allowed to take the law into their own hands," Azim said.

The sweeps mirrored tactics used to ensure no crowds turned out to welcome Sharif when he tried to return from exile two weeks ago. Hundreds of opposition activists were briefly jailed to prevent them reaching Islamabad's airport. Sharif was swiftly expelled to Saudi Arabia.

Musharraf's popularity and power have eroded since his botched effort to fire the Supreme Court's chief justice earlier this year. His administration is also struggling to contain a surge in Islamic militancy.

Musharraf has called for moderate political forces to unite to defeat extremism and has held talks on a possible power-sharing deal with former Prime Minister Benazir Bhutto, who has vowed to return home Oct. 18 after eight years of self-imposed exile.