ISLAMABAD — A longtime loyalist of a slain opposition leader, Benazir Bhutto, was elected Pakistan’s new prime minister today and immediately freed judges detained by President Musharraf.

The release of the judges was a powerful symbol of Mr. Musharraf’s slipping authority since Bhutto’s party swept parliamentary elections last month.

The newly elected prime minister, Yousaf Raza Gilani, will form a new government dominated by Mr. Musharraf’s foes, who have vowed to slash the American-backed president’s sweeping powers and review his counterterrorism policies.

Minutes after parliament elected Mr. Gilani, dozens of political activists and lawyers climbed over a wall surrounding the home of the deposed chief justice, Iftikhar Mohammed Chaudhry, who had been under house arrest since November.

Justice Chaudhry emerged onto a balcony smiling and thanked supporters in his first public appearance since his detention. Riot police stood by as the intruders rallied on the justice’s front lawn.

The National Assembly voted 264-42 to elect Mr. Gilani, who told lawmakers he would demand the release of all judges detained under Mr. Musharraf. Soon afterwards, a deputy Islamabad commissioner, Amir Ahmed, said Mr. Gilani’s order had been implemented, Pakistan’s state-run news agency reported.

After the vote, Mr. Gilani shook hands with Bhutto’s son, Bilawal Bhutto Zardari, who wiped tears from his face and smiled. His mother held the post of prime minister twice before being killed in a suicide attack in December.

Cheers of “Long live Bhutto, BB is still alive!” rang out through parliament. Fellow lawmakers embraced Mr. Gilani as he made his way to the prime minister’s lectern.

“Democracy has been revived due to the sacrifice of Benazir Bhutto,” Mr. Gilani told lawmakers. “We didn’t get here out of charity. This moment came because of continued struggle and martyrdom.”

The new government has promised to reinstate Justice Chaudhry and other senior judges within 30 days — a move that could trigger a power struggle with Mr. Musharraf, a former army chief who seized power in a 1999 coup. Some believe it could prompt him to resign.

“I have no words to thank you for the way you struggled for nearly five months for the enforcement of the rule of law and our constitution,” Justice Chaudhry said from his balcony.

Mr. Gilani, who will be sworn in tomorrow by Mr. Musharraf, said his first act as prime minister would be to seek a parliamentary resolution demanding a U.N. probe into Bhutto’s assassination.

He will head an administration facing mounting economic problems, including double-digit inflation, power shortages, and sagging foreign investment.

Followers of another former prime minister, Nawaz Sharif, hold the second-largest number of seats in parliament.

Observers say Mr. Gilani’s record and treatment at the hands of Mr. Musharraf make him a good pick to straddle the rivalry and ideological differences inside a coalition that includes Islamists and ethnic Pashtun nationalists, as well as the country’s main center-left and center-right parties.

“Mr. Gilani is a man who suffered from Musharraf’s martial law,” a lawmaker for one of the four parties that agreed to form a new coalition government, Ahsan Iqbal, said. “He understands well that getting rid of dictatorship is important.”