CAIRO, Egypt – In a major step toward multicandidate presidential elections, parliament overwhelmingly passed a constitutional amendment proposed by President Mubarak yesterday amid calls for reform during his 23-year authoritarian rule.

Parliament, a 454-seat house dominated by Mr. Mubarak’s National Democratic Party, had been expected to adopt the amendment. A referendum will follow, possibly later this month, to ratify the amendment. The election is scheduled for September, but the 77-year-old Mr. Mubarak has yet to announce whether he would seek a fifth, six-year term.

Mr. Mubarak has so far been elected in simple “yes” or “no” votes in which he was the sole candidate. He proposed opening the door to other candidates for president in a surprise announcement in February.

Parliament approved the amendment first by a show of hands and later by an official roll call, with 405 deputies voting in favor and two abstaining. Speaker Fathi Sorour did not say how many voted against the measure, but at least 20 opposition and independent deputies were seen leaving the chamber during the roll call.

The amendment needed 303 deputies, or two-third of house members, to pass.

It ran into fierce opposition by political parties, reform groups, and judges over what they saw as the crippling conditions set for independents who want to run against Mr. Mubarak and the lack of guarantees for a clean vote.

Major opposition parties voiced strong objections to amendment during debate yesterday in a session that lasted nearly four hours and was held amid extraordinary security.

Mr. Mubarak’s February announcement has plunged Egypt into political uncertainty deepened by a flurry of unprecedented street protests and repeated American calls for the introduction of reforms. On its part, Mr. Mubarak’s government has cracked down on the outlawed Muslim Brotherhood, arguably Egypt’s largest opposition group, rounding up hundreds of its members. It also has rebutted calls for the repeal of emergency laws in force since 1981.

“This is a constitutional massacre,” an independent deputy, Abdel Azeem Maghrabi, said during the debate, which was broadcast live on state television. “Enough, enough, enough!”

But a stalwart of Mubarak’s party and a staunch supporter of the regime, Kamal el-Shazli, expressed support for the amendment.

“We still need Mubarak and we still need Mubarak’s purity,” he declared.

The leader of the Tomorrow party who has declared his candidacy, Ayman Nour, rejected the draft. “We returned to zero point,” he said.

The only deputy from the Nasserite party, Haider Baghdadi, was immediately dismissed from his party when he told the house that he had no objections to the draft.

The amendment to the constitution’s Article 76 initially stipulated that independents must get 300 recommendations from elected members of the lower and upper houses of parliament and city councils, all of which are dominated by Mr. Mubarak’s party, before they are cleared to enter the race. The approved amendment lowered this to 250.

Opposition political parties, whose popular base have greatly diminished in recent years, were exempted from these conditions, according to a text of the draft published in the local media.

Less than a mile away from the parliament building in downtown Cairo, the opposition Kifaya, or “Enough” group, called for a boycott of the presidential election, labeling it “theatrics” and a “farce.”

In a statement, it accused the government of desperate maneuvers aimed at “aborting people’s hopes for freedom and democracy.” Kifaya is a growing activist movement calling for an end to Mr. Mubarak’s rule and far reaching political reforms.

Dozens of Mr. Mubarak’s supporters rallied in the same downtown area, raising the president’s picture and chanting, “We protect Mubarak with our soul and blood!” and “Long live Mubarak, long live Egypt!”

Some of the pro-Mubarak demonstrators wore stickers declaring “Yes to Mubarak” and “Not enough.”

“I love Hosni Mubarak. … He is a father to all Egyptians,” a 28-year-old government employee, Ahmed Eied, said.