CAIRO — After years of the government’s promising to end Egypt’s state of emergency, Parliament on Tuesday approved a government request to extend for two years its right to arrest people without charge, detain prisoners indefinitely, limit freedom of expression and assembly, and maintain a special security court.

In an unusual case of public outreach by Egypt’s normally tight-lipped leaders, the government took pains to explain its decision and announced that the emergency law — in place continuously since President Anwar el-Sadat was assassinated in 1981 — would be used only in cases of terrorism and drug trafficking. Officials also said that some provisions of the law would be dropped.

But the concept of terrorism is so broad in Egyptian law and the language in the new measure so malleable, that the government decision was immediately criticized by human rights groups, political activists and independent human rights monitors, who say they expect little to change in a nation that routinely uses the heavy hand of the police and prisons to silence political opposition.

“Even the claim that emergency powers will now be limited to terrorism and drug trafficking cases only is false,” said Hossam Bahgat, executive director of the Egyptian Initiative for Personal Rights. “More dangerously, the culture of exceptionalism stays, and with it the message that security agencies are still above the law.”

The government’s announcement, and its unusually aggressive effort to explain and mitigate the impact of its decision, comes at a time of rising political and social uncertainty in Egypt. Elections for the upper house of Parliament are to be held in a few weeks, the lower house in the fall and the presidency next year.

The government is also facing rampant rumors concerning President Hosni Mubarak’s health; daily protests by workers demanding better wages; and a reinvigorated political opposition energized by the former United Nations chief nuclear monitor, Mohamed ElBaradei, who has said he might run for president.

In Washington, the State Department spokesman, Philip J. Crowley, said: “We are disappointed. We have questions about how this fits with pledges that the government of Egypt has made to its own people to try to find a way to move beyond the emergency law.”

Prime Minister Ahmed Nazif told Parliament that language had been added to ensure that that the law would be used only to protect against terrorism and narcotics trafficking. He also announced that for the first time, the government would limit its emergency powers under the law, nullifying provisions that allowed for censorship and shutting down publishers and broadcasters, monitoring of all forms of communication and confiscation of property.

The prime minister tried to explain why the government had not been able to fulfill a promise made by Mr. Mubarak in 2005 to replace the emergency law with specific antiterrorism legislation. He said that the government was having difficulty finding the proper balance between protecting the nation and preserving civil liberties, comparing the challenge to President Obama’s difficulties in closing down the prison at Guantánamo Bay and comparing the law to the Patriot Act, adopted in the United States after Sept. 11, 2001.

The government also pointed to bombing attacks in the Sinai Peninsula and the recent prosecution of a Hezbollah cell convicted of planning terrorist acts in Egypt as evidence of the need for preserving the emergency law.

That explanation, however, did little to blunt the avalanche of criticism. “Of course it is a blow that they have renewed the emergency law yet again,” said Martin Scheinin, the United Nations special representative on human rights and terrorism, who conducted a fact-finding mission in Egypt in April 2009.

Some critics noted that Egypt had insisted for years that it used its emergency powers only to combat terrorism.

“They always claimed that the emergency law is used only against drug traffickers and terrorists,” said Aida Seif El-Dawla, a human rights advocate who works with victims of torture and abuse. “They have been systematically lying.”

In a report presented to the United Nations Human Rights Council in 2009, Mr. Scheinin wrote that Egyptian law defines terrorism to include not only violent acts but also “ ‘any threat or intimidation’ with the aim of ‘disturbing the peace or jeopardizing the safety and security of the society.’ ” In addition, he wrote that Egyptian terrorism-related law “contains a wide range of purposes, such as ‘to prevent or impede the public authorities in the performance of their work.’ ”

Sarah Leah Whitson, director of the Middle East and North Africa for Human Rights Watch, added that while the government said it agreed not to use the law to monitor communications, it could do so under amendments to the Constitution that allow for the establishment of a permanent antiterrorism provision, which would allow such monitoring.

“This claim that the source and need for the emergency law has to do with terrorism is transparently false,” Ms. Whitson said. “In fact they use this law to prosecute any political activist who criticizes the government.”

Moufid Shehab, the minister of legal and parliamentary affairs, acknowledged that the law was not precise and that it had been used in a more general fashion. But he said that issue was not strictly one of definition, but implementation by the police, who he said are already being trained to be more aware of human rights.

The government also said judicial supervision would also help prevent abuses. But in practice, the security services often operate free from effective oversight, legal experts said.

In a report presented in March to the United Nations Human Rights Council in Geneva, Mr. Scheinin, a professor of public international law, said that court decisions to release prisoners from administrative detention were often ignored or that the prisoners were released and immediately rearrested.

“Basically there is no legal certainty as long as there is an emergency law in place,” Mr. Scheinin said.