Qazi Hussain Ahmad, the chief of a six-party coalition, was placed under house arrest in the eastern city of Lahore.
Other senior leaders were either arrested or asked not to leave their homes in Islamabad, where the rally against the publication of cartoons of prophet Muhammad was to be held on Sunday.
The cartoons are deemed to be blasphemous by Muslims.
Mian Maqsood, a spokesman for the coalition said hundreds of Muslim leaders had been arrested, although Aftab Khan Sherpao, the interior minister, said only about two dozen had been detained to stop the latest protest against the publication of the cartoons in Europe and elsewhere.
The arrests came hours after the government warned Islamic groups against holding the rally, fearing it would spark more violence after at least five people died in riots across the country over the past week.
Security stepped up
On Sunday, soldiers and police were on alert in Islamabad.
Pakistani intelligence officials have said members from outlawed groups have been stirring up the violence.
Qazi Hussain Ahmad (C) has been
placed under house arrest
The authorities have banned demonstrations in several cities in the country's east, where riots turned deadly last week.
Sheikh Rashid Ahmed, the information minister, said late on Saturday: "We have condemned these blasphemous cartoons, but we will not allow anyone to disrupt peace."
But the rally's organisers said they will defy the order and go ahead with the protest.
Mian Mohammad Aslam, a lawmaker with a coalition of six religious parties, said: "Our supporters are being arrested by police in raids at their homes, but we will hold the rally as planned."
Aslam was also arrested just before dawn on Sunday.
The cartoons offend Muslims because Islamic tradition bars drawings of the prophet Muhammad, favourable or otherwise, in a policy to discourage idolatry.
The drawings were first published in the Danish newspaper, Jyllands-Posten, and then reprinted by European media outlets that insist they are exercising their right to free speech.
Thousands have participated
in protests in Pakistani cities
Also on Saturday, about 12,000 women joined a peaceful protest in the southern city of Karachi.
The event was organised by Jamaat-e-Islami - the country's oldest and best-organised religious party.
Aysha Munawar, a senior leader of the party, told the crowd: "We want that those who drew these blasphemous cartoons be hanged."
She urged the government to sever ties with countries where the cartoons have been reprinted.
Lawmaker Ghaffor Ahmad, another leader of the group, said in a speech that police and the army should join the protests.