Egypt's main Islamist party and other opposition groups are strengthening their appeal by using images of desperate Palestinians streaming out of the Gaza Strip to provoke wider protests against President Hosni Mubarak's 26-year-old government.

Demonstrations in Cairo and throughout the country by the Muslim Brotherhood and other political groups ostensibly have been staged to declare Egyptian solidarity with the residents of Gaza. But they are also aimed at weakening Mubarak, whom the groups accuse of oppression and criticize for economic shortcomings and close ties to Washington.

It is political theater punctuated with dangerous rhetoric. Mubarak's vast intelligence and security forces are attempting to prevent pro-Palestinian protests from erupting into sustained nationwide anti-government rallies. But the Muslim Brotherhood and Kifaya, Arabic for "Enough," an umbrella opposition group of leftists and nationalists, are determined to make just that happen. The Muslim Brotherhood has sponsored 80 demonstrations since Wednesday, when hundreds of thousands of Gazans began pouring into Egypt through a breached border wall.

The Muslim Brotherhood, which favors a government guided by Islamic law, known as Sharia, has a platform of nonviolence but has been accused over the years of bombings and other militant acts.. Despite the arrests of hundreds of its members, the group enjoys extensive support among the poor and middle class and poses the nation's most significant political threat to Mubarak's ruling National Democratic Party.

The Palestinian cause is the crystallizing passion in the Arab world, but the Gaza border crisis has brought new urgency to a public relations battle between Islamists and secular governments, especially in Egypt. It has also demonstrated that Hamas, the militant Islamist party that controls Gaza and is ideologically linked to the Muslim Brotherhood, remains a major factor in the future Palestinian equation, contrary to the wishes of the U.S., Egypt, Israel and the Palestinian Authority.

At the Rafah border crossing Monday, Hamas cooperated for the first time with an Egyptian effort to reassert control over the frontier. Egyptian guards and Hamas forces coordinated security and used concrete and barbed wire to close at least two gaps in the barrier opened by explosions. At least four gaps remained open, including two for cars.

Thousands of Palestinians went back and forth. Traffic, thinned by rain Sunday, was heavier Monday but down from last week's massive levels. Shoppers, however, found little to buy in the Egyptian Sinai, where prices began rising and the government limited the availability of goods.

While Egyptian authorities debated how to further shrink the number of Palestinians in Sinai, they also concentrated on domestic dissent. Police in recent days have broken up a number of protests and arrested scores of Muslim Brotherhood members and Kifaya activists.

Opposition groups in Egypt have historically been disparate, with various religious and secular agendas and lacking a unifying spirit other than disdain for Mubarak's government, which receives nearly $2 billion a year in U.S. aid and upholds an unpopular peace treaty with Israel.

The current political maneuverings between the government and opposition come as this nation of 73 million people is enduring persistent inflation, shrinking government subsidies and budget deficits.

The outlawed Muslim Brotherhood, whose members ran as independents and won about 20% of the seats in Parliament in 2005, said its chief aim is to support Palestinians and condemn U.S. and Israeli policies. But the organization acknowledged that the protests had grown wider in scope. Banners in a Cairo demonstration of 2,000 protesters last week included slogans sympathetic toward Palestinians and vitriolic against Egypt, such as "A Country Without Justice."

"The regime dealt brutally with demonstrators because it is concerned about domestic stability," said Abdel Moneim Abul Fotouh, a Muslim Brotherhood leader. "The regime knows that there is public outrage for other reasons including inflation, unemployment and other accumulated problems. It fears that things will explode."

Egyptians are "terribly depressed by the domestic situation and want to express themselves by any means," said George Ishaq, a Kifaya leader. "They seized [the Gaza border dispute] as a chance to express their views."

Mohammed Sayed Said, deputy head of the Al Ahram Center for Political and Strategic Studies in Cairo, said support for the Palestinians is giving the Muslim Brotherhood "a great deal of legitimacy."

"They're anti-Israeli and anti-American. They see themselves as the most vehement resistors, and this is a big payoff for them. They have been very clear in focusing on the Palestinian issue," he said.

Mubarak, for his part, is attempting to show that he is just as roused as the Islamists over what he calls Israel's "collective punishment" of Palestinians. The president criticized Israel for retaliating against Hamas missile strikes with a fuel blockade of Gaza; days later, Hamas blew the holes in the border wall. Mubarak has received praise across the Arab world for allowing upward of 500,000 Palestinians to shop for supplies and unwind in Sinai.

The main problem the 79-year-old Mubarak faces in the Arab street, however, is his grudging support of U.S. and Israeli policies that isolated Hamas after the group seized Gaza from Fatah, the faction of Palestinian Authority President Mahmoud Abbas. Egypt was wary of Hamas exporting militants, but the containment strategy, which included economic sanctions, failed.

The Rafah crossing was largely open until militants burrowed under Gaza's border with Israel and captured Israeli Cpl. Gilad Shalit in June 2006. The Israelis tightened Gaza's borders in response. A year later, when Hamas fighters routed Fatah forces and took control of Gaza, the frontier was sealed.

"You cannot go back to that same policy," Said said. "Egypt does not want to recognize Hamas as a legitimate government in Gaza. But you just can't leave a total vacuum. Egypt's concerned about extremists, but you can't clash with Palestinians [crossing the border]. You don't want to look like Israel at all."

A slight readjustment appears to be underway. Aside from cooperating on limiting border traffic Monday, Hamas is expected to send a delegation to Egypt on Wednesday to discuss ending the crisis. That's the same day officials from the rival Palestinian Authority, whose forces Mubarak would prefer control the border crossing, will travel to Cairo for a separate meeting.

A central question in coming months will be Egypt's long-term relationship with Hamas and how the militant group will fit into a new Palestinian-Israeli peace initiative spurred by the Bush administration. Most Egyptians are skeptical of the peace effort, regarding it as a hurried plan by a lame-duck U.S. president that may embarrass their nation and other regional U.S. allies.