RAMALLAH, West Bank – Palestinian Arabs marked the fourth anniversary of their uprising yesterday amid signs that the terrorist Hamas group is preparing a political challenge to Yasser Arafat despite a series of Israeli military blows at the terror group’s leadership.

Hamas published newspaper ads urging supporters to vote in upcoming municipal elections, saying “It’s time for change.” And a top Hamas leader indicated the group might try to unseat Mr. Arafat in presidential elections, which have not yet been scheduled.

Meanwhile, Palestinian Arab terrorists released Riad Ali, an Arab-Israeli television producer for CNN, a day after his abduction in the Gaza Strip. It remained unclear why he was taken hostage.

The kidnapping, coupled with Hamas’ electoral challenge, were apt reflections of the state of affairs in the West Bank and Gaza Strip after four years of fighting with Israel.

It was not clear whether his kidnapping Monday signaled a new practice by Palestinian Arab terrorists – perhaps an attempt to copy Iraqi terrorists who have snatched dozens of foreigners – or whether Mr. Ali was taken for personal or local reasons.

Talking to reporters after emerging from a Gaza police station, Mr. Ali refused to discuss what demands his abductors made, but said they identified themselves as members of the Al Aqsa Martyrs Brigades, which is linked to Mr. Arafat’s Fatah movement. Al Aqsa spokesman Abu Mohammed denied the group was involved.

The violence has left Mr. Arafat’s Palestinian Authority severely weakened, leading to widespread chaos and boosting Hamas’ popularity.

“We need an evaluation of these four years,” Prime Minister Qurei said. “Where have we been right and where have we been wrong? What did we achieve and what didn’t we achieve?” Mr. Qurei also called on Israel to reassess its policies.

The uprising erupted on September 28, 2000, after Ariel Sharon, then Israel’s opposition leader, visited a sensitive Jerusalem hilltop revered by both Jews and Muslims. Palestinian Arab riots broke out, and five months later Mr. Sharon defeated Ehud Barak in a special election for prime minister.

Last night, about 30 Israeli tanks moved into northern Gaza and fired several shells, witnesses said. The military said the purpose was to try to stop terrorists from shooting rockets at nearby Israeli towns. Earlier, the Israelis blew up a building next to the Gaza settlement of Netzarim, saying it contained a tunnel used by militants. No casualties were reported in either incident.

Israel appears to have gained the upper hand in the fighting. It has confined Mr. Arafat to his West Bank headquarters for three years and killed hundreds of leading terrorists. The Palestinian economy is in tatters.

In a sign of weariness, a recent opinion poll by An-Najah University found that two-thirds of Palestinian Arabs support a cease-fire with Israel.

“The uprising has not been defeated, but it has not brought victory. Frankly, it is now closer to defeat than victory,” commentator Hani al-Masri wrote in the Palestinian daily Al Ayyam.

Mr. Sharon has abandoned peace talks with the Palestinian Arabs and instead launched a “unilateral disengagement” plan meant to separate the two peoples. The plan includes building a security fence to separate Israel from the West Bank and making a complete pullout from Gaza next year.