Saturday, 52 days after it began, the social protest movement will face its most important test so far, the March of the Million.

The leaders, activists and organizations behind the movement are working hard to get the masses into the streets Saturday night. The protest has had its up and downs. It has garnered public support on a scale that sometimes surprised even the leaders, but it has also flagged a bit, and its inexperienced organizers have also made mistakes that jeopardized its future. It is obvious to all that Saturday night is crucially important.

The main event will begin at 9:30 P.M. at Tel Aviv's Kikar Hamedina. It will be preceded by a march from Habima Square via Marmorek, Ibn Gvirol and Jabotinsky streets. The rally will be addressed by the initiator of the tent protest, Daphni Leef; National Student Union chairman Itzik Shmuli; Motti Ashkenazi, who led the public protest after the 1973 Yom Kippur War; Vicki Knafo, leader of the single mothers' protest in 2003; Dr. Shiri Tenenbaum, as representative of the medical residents; and novelist Eshkol Nevo.

The featured musical performers are singer Eyal Golan and two groups, Hayehudim and Hadag Nahash. Shalom Hanoch was scheduled to appear, but canceled Thursday "due to scheduling issues." The cast of the television program "Eretz Nehederet" ("A Wonderful Country" ) are slated to present a satirical sketch created especially for the rally.

The organizers and the Israel Police are expecting a few hundred thousand people to come to Kikar Hamedina. Student union officials said Thursday that engineers have estimated around 400,000 people could fit into the square and the surrounding streets.

The proceedings will be broadcast live on a giant screen that will be mounted on the roof of one of the buildings ringing the square, as well as smaller screens installed throughout the area. Four amplifier towers will also be erected.

The head of the student union's logistics operations, Yuval Bdolah, said he expects the rally will be unlike any event in Israeli history. He noted that the entire production staff, including the stage workers and audiovisual companies, are volunteering their services or working at cost, and cited the close cooperation of the police.

Hundreds of police officers will provide security. Many streets in Tel Aviv will be partially or completely closed, starting at 5:30 P.M. Saturday.

The march route, Kikar Hamedina itself and the surrounding streets will be closed to vehicular traffic. Ibn Gvirol Street will be closed to all vehicles in both directions. The following streets will be closed to eastbound traffic: Jabotinsky, Arlosoroff, Ben-Gurion and Gordon, from Ben-Yehuda to Ibn Gvirol; Dizengoff and Hanevi'im, from Hamelekh George to Ibn Gvirol; Kaplan and Hahashmona'im, from Derekh Petah Tikva to Ibn Gvirol; Carlebach, from Hahashmona'im to Ibn Gvirol.

Rothschild Boulevard will also be closed to traffic between Hahashmona'im and Marmorek streets, with additional closures as needed.

The Arlosoroff, Hashalom, Hahalakha and Rokach exits from the Ayalon freeway may be blocked as needed to control traffic.

Police officials have said they will not permit demonstrators to block streets and impede traffic after the rally, as has happened after some demonstrations in the past several weeks.

Additional demonstrations will be held Friday evening around the country. The Jerusalem rally will be held near the prime minister's residence. Speakers will include actress Orna Banai, while Izhar Ashdot, Karolina and the Ma Kashur comedy trio will provide entertainment.

Revital Hoval contributed to this report.