ISLAMABAD, Pakistan — The ruling by the Supreme Court Wednesday barring opposition leader, Nawaz Sharif, from holding elected office plunged Pakistan into political crisis as Mr. Sharif called for nationwide protests and the president imposed executive rule in the important province of Punjab.
The confrontation between the president, Asif Ali Zardari and Mr. Sharif, was likely to serve as a distraction from the escalating Qaeda and Taliban insurgency that Washington is trying to persuade the government to focus on, political analysts said.
Soon after the court decision, supporters of the Pakistan Muslim League-N, the political party headed by Mr. Sharif, burned tires and ripped down posters of Mr. Zardari in Lahore and Rawilpindi.
By early evening, the chamber of the Punjab assembly was filled with Muslim League legislators chanting slogans and banging the desks.
The Supreme Court disqualified Mr. Sharif, who served as Prime Minister twice in the 1990s, from holding public office because of a criminal conviction connected to the military coup that ousted him from office in 1999.
In an attempt to forestall the coup, Mr. Sharif had ordered that an aircraft carrying Gen Pervez Musharraf into Pakistan not be allowed to land. Mr. Sharif was convicted on hijacking charges and forced into exile in Saudi Arabia.
The court also barred Mr. Sharif’s brother, Shahbaz, from holding elected office, leading him to immediately step down as Chief Minister of the Punjab.
Nawaz Sharif denounced the court decision as a politically motivated ruling orchestrated by his archrival, Mr. Zardari. “It’s an edict not a verdict,” Mr. Sharif said.
He added that Mr. Zardari had tried to offer a business deal to his brother, Shahbaz Sharif, in exchange for support of the Supreme Court that Mr. Sharif has deemed illegal.
Hours later, President Zardari retaliated, ordering the governor of Punjab, Salman Taseer, a member of the president’s political party, to administer the province for two months until the appointment of a new chief minister.
Punjab is the heartland of popular support for the Sharif brothers and is the most populous province in Pakistan.
Nawaz Sharif does not enjoy as much popularity in Pakistan’s other three provinces, and one of the tests in the coming weeks will be whether he can muster significant support outside Punjab.
The appointment of Mr. Taseer, a major ally of the president, to oversee the province appeared aimed at trying to weaken the hold of the Sharif brothers over the bureaucracy and key law enforcement posts.
The ruling by the Supreme Court against the Sharif brothers had been anticipated for some weeks. Their assessment that the court decision was political rather than judicial had also been expected.
The Pakistan Peoples Party said in a statement that the ruling was “a court decision and has nothing to do with the government.” It urged the Sharif brothers “to control their supporters in the interest of democracy.”
A spokeswoman for the government, Sherry Rehman, said: “It’s unfortunate the ferocity of the reaction and the personalized attack on the president has soured the atmosphere.”
She urged the Sharif brothers to join the government in the spirit of “reconciliation” to tackle the economic problems facing the country.
The standoff between Mr. Zardari and Mr. Sharif was considered so combustible that the “government’s future is uncertain,” said Hasan Askar Rizvi, a columnist for the Daily Times, an English language newspaper that is owned by Mr. Taseer. But it would take at least a month to see an outcome, he said.
The Obama administration, which is currently conferring with the Pakistani government on new strategies to fight the insurgency, would be “very concerned and upset” by the political turmoil, Mr. Rizvi said.
The prospect of a popular movement stirred up by Mr. Nawaz was worrying because in the past such efforts in Pakistan had “always resulted in a system that isn’t democratic,” Mr. Rizvi said.
Among the factors adding to the political volatility were the relative showings of Mr. Zardari and Mr. Sharif in recent public opinion surveys.
According to a poll taken in October and released in December by the International Republican Institute, a Washington based outfit affiliated to the Republican Party, Mr. Sharif’s approval ratings outstripped Mr. Zardari by large margins.
When asked who they would prefer to have as president, 59 percent of the respondents said they preferred Nawaz Sharif, and 19 percent said they preferred Mr. Zardari.
The poll was taken among 3,500 people between Oct. 15 and Oct. 30 in the four provinces of Pakistan, according to Robert Varsalone, the manager of the survey. The error of margin was 1.66 percent, he said.
After the ruling Wednesday, Nawaz Sharif said he would join a protest march of the lawyers’ movement on March 12. It is intended to draw attention to the dismissal of the Chief Justice Iftikhar Mohammed Chaudhry two years ago.
Mr. Sharif has argued that Mr. Zardari was intent on keeping the current Chief Justice Abudl Hameed Dogar, who was appointed under an emergency decree during the Musharraf era, because Mr. Dogar would protect an amnesty on corruption charges that included Mr. Zardari and his wife, Benazir Bhutto.
Mr. Zardari adamantly rejected the argument and refused to reappoint Mr. Chaudhry last year. Nawaz Sharif left the coalition government over the issue last fall. The ruling Wednesday was issued by the Musharraf-appointed court, which Mr. Sharif has opposed and which Mr. Zardari has supported.