CAIRO, Egypt — Many polling stations stood virtually deserted yesterday as Egypt held a referendum on constitutional amendments that opponents have condemned as a sham and a setback to democratic progress.

Opposition parties called for a boycott of the referendum, but turnout was also hurt by widespread apathy and confusion over the changes, which were pushed to a public vote only a week after they were approved by parliament.

“I swear to God, I don’t know what I’m voting for,” said Hassan Abdel Salaam, a house painter casting his ballot at a Cairo polling station. “If I didn’t vote, maybe I would get into trouble. I have five children, and we live in one room.”

At several stations, the government bused in public employees to cast ballots, and state-run news outlets ran messages urging voters to turn out. In one Cairo district, a truck plastered with posters of President Mubarak blared messages through a loudspeaker calling on residents to vote “for the sake of your children and your future.”

Mr. Mubarak’s government has touted the changes as part of a campaign of democratic reform. But opponents say the amendments will only cement his party’s control, pointing to provisions they say will weaken monitoring of elections and allow vote-rigging. One amendment will allow the suspension of civil rights like requirements for arrests and search warrants in terrorism investigations.

In a televised address Sunday, Mr. Mubarak urged Egyptians to vote, saying the amendments “give a new push to political party activity” and would “stop the exploitation of religion and illegal political behavior, and protect the homeland from the danger of terrorism.”

His son, Gamal, a top leader of the ruling National Democratic Party, also called for a large turnout, saying Sunday that the 34 amendments were a “very important step in our march toward further reform on the political side.”

A tour of polling centers in Cairo showed turnout to be very low. In one district of 1,000 registered voters in Cairo’s Heliopolis neighborhood, poll workers said only 40 ballots had been cast by early afternoon. The Egyptian Organization for Human Rights estimated that only 2% to 3% of the electorate had voted by 2 p.m.

The Egyptian Organization for Human Rights reported rigging in hundreds of polling stations. In the Nile Delta province of Damietta, for instance, civil servants were seen stuffing ballot boxes in a station where the attendance register showed only one person had voted, the organization said.

Information Minister Anas el-Fiqqi said the voting was taking place in “complete transparency.”

Police arrested a number of members of the opposition Muslim Brotherhood and the secular Al-Ghad Party yesterday for “disturbing the peace” when they urged voters at polling stations not to cast ballots, police officials said, speaking on condition of anonymity as they were not authorized to talk to the press. They did not specify how many were arrested.

The night before the vote, police arrested six Al-Ghad Party members and raided party offices in Cairo, Alexandria, and the northern Delta, police said.

In the southern Cairo district of Helwan, dozens of workers from state-owned military factories were bused to a polling station. Military Production Minister Sayid Mashaal arrived at the station in a motorcade of five black Mercedes cars to ensure they cast ballots.

One factory worker, Magdy Fadail, refused to oblige and tore up his voting card in front of the Associated Press. “What should I vote for?” asked Mr. Fadail, who works for a military-goods company. “They ship us like animals in cars so we get in and say yes.”

But others said they voted in favor of the measures. Mohammed Ali Hassan, 62, shoemaker, said he wanted to endorse the new security measures.

“The issue of terrorism has risen here many times, and now police will have the right to storm any place they suspect,” Mr. Hassan said. Opposition supporters sent thousands of cell-phone messages urging a boycott, with texts such as: “Your vote is too precious to be cast in the phony referendum.” The paper of the Al-Ghad Party ran the headline: “Even monkeys in the zoo know the referendum is forged.”

The Muslim Brotherhood had said it would stage demonstrations despite a government ban. But on Friday, Brotherhood leaders stepped back from the protest call, apparently fearing a crackdown.

Riot police waited in trucks in central Cairo, ready to be deployed quickly.