CAIRO, Egypt — An opposition lawmaker who had called for democratic elections in Egypt to put an end to decades of unopposed rule by President Hosni Mubarak was sent to jail yesterday for 45 days, hours before the start of a long-awaited "national dialogue" on Egypt's political future.

The abrupt arrest of Ayman Nour on forgery charges comes amid a mounting debate over Mubarak's seemingly open-ended run as president, along with a fresh discontent sparked by speculation that the president hopes to pass the job to his son someday.

As head of the al-Ghad (Tomorrow) party, which was formed last fall, Nour had pushed for constitutional reform, an open election to replace the yes-no referendums that have repeatedly sent an unopposed Mubarak back to office, and a freer debate.

The government has accused Nour of faking all but 14 of the thousands of signatures he collected to win permission to form his party.

The 45-year-old lawmaker's parliamentary immunity was lifted over the weekend, and security officers raided his home, seizing computers and files.

He told the judge yesterday that his arrest would "hinder the democratic process and reform in Egypt." He told an Egyptian rights group that he had been beaten during his arrest.

In Washington, a State Department spokesman said the United States was concerned about the arrest of Nour.

"He is one of Egypt's most prominent opposition leaders," said spokesman Richard Boucher. "The arrest, in our mind, raises questions about the outlook for a democratic process in Egypt."

The political mood in Egypt has been particularly tense in recent months. Mubarak, 76, who has ruled since the assassination of Anwar Sadat in 1981, has hinted that he'll stand for a fifth term in a referendum later this year.

Many Egyptian observers believe that Mubarak's son Gamal is being groomed for an eventual handover of his father's office.

Neither prospect sits well with many Egyptians, who have become more outspoken in recent months against Mubarak's hold on power. Opposition figures have grown more insistent in their calls for constitutional reform. Protesters took the bold step of demonstrating in the streets this winter against Mubarak's re-election.

Nour had been among the more vocal critics. Ahead of the national-dialogue talks on reform being held this week between opposition parties and Mubarak's ruling party, he fired off a letter to the ruling party.

He called for Mubarak to participate in the debate and for the discussions to be open to the public. Since being recognized in October, the al-Ghad party has gained thousands of members, its leaders say.

The party has just bought a new headquarters, and its newspaper is expected to go to print for the first time this month.

During the national dialogue, opposition parties repeated calls for changes to Egypt's constitution, under which parliament nominates one presidential candidate — in effect ensuring incumbents stay in power. They also called for the abolition of emergency laws in place since 1981.