Updated

Confident of victory in Tuesday's election, Prime Minister Ariel Sharon withdrew to his office on the last day of the campaign, while opposition leader Amram Mitzna phoned wavering voters in a desperate attempt to cushion what is shaping up as the worst-ever showing of the once-dominant Labor Party.

Violence continued into the early hours before polls opened. An explosion leveled a house in Gaza City, killing three Palestinians, including a teenage brother and sister, early Tuesday and wounding 11 others. Witnesses and Palestinian security officials said an Israeli military helicopter had been circling the area for several hours and apparently fired a missile at the building.

Israeli military sources, speaking on condition of anonymity, said the blast was caused by premature explosion of a bomb being assembled by militants in the house and not from an Israeli attack.

Israel's fourth election in seven years has inspired little passion, even though the direction of Israel's conflict with the Palestinians is at stake. Mitzna champions a quick withdrawal from the Gaza Strip and much of the West Bank, while Sharon says troops must stay there until Palestinian militants have been crushed.

Many voters have simply despaired of a quick end to 28 months of fighting that has killed more than 2,800 people, three-fourths of them on the Palestinian side.

"No one really expects the dawn of a new day -- at most the twilight of an old evening," commentator Hemi Shalev wrote in the Maariv daily. "It is likely ... that what was, will be."

About 4.7 million of Israel's 6.6 million citizens are eligible to vote, with 27 parties competing for 120 seats in parliament. The nearly 8,000 polling stations are to open at 7 a.m. local time Tuesday (midnight EST) and close at 10 p.m. (3 p.m. EST). At that time, three Israeli TV stations plan to broadcast exit polls or telephone surveys. Complete returns are expected Wednesday, and official results will be announced Feb. 8.

Israel clamped a three-day closure on the Palestinian areas, further tightening travel bans amid a flurry of warnings that Palestinian militias will try to disrupt the vote.

In Cairo, the Palestinian militant groups Hamas and Islamic Jihad announced Monday they will not halt attacks on Israeli civilians, ending Egypt's months-long effort to pave the way for a truce and resumption of peace talks. There had been some expectation that a truce announcement could be made before Israel's vote.

With Sharon's right-wing Likud expected to emerge as the largest faction -- Monday's polls had Likud winning 30 to 33 seats -- attention has already shifted to post-election coalition troubles that could significantly weaken the prime minister.

Mitzna has rebuffed Sharon's appeals to bring Labor into a Likud-led government. "A promise is a promise," Mitzna, 57, said Monday, reaffirming his pledge not to renew his party's 20-month alliance with Sharon that fell apart in November.

Without Labor, Sharon, 74, would have to form a coalition of right-wing and Jewish religious parties. Polls predict such a lineup would have a narrow majority in parliament, but would be unstable because it makes Sharon vulnerable to political blackmail.

A wild card is the upstart Shinui, which is expected to become the third-largest party and says it will join only a Likud-Labor alliance that does not include religious parties.

The mood in the Mitzna camp was subdued Monday, and the Labor leader spoke openly about the possibility of defeat; polls predicted 18 to 19 seats for Labor, down from 26 in the 1999 election. Commentators said that if Labor got fewer than 20 seats, Mitzna was in danger of being deposed as leader.

"We will struggle until victory," Mitzna said during a campaign stop in the Tel Aviv suburb of Ramat Hasharon. "If we don't succeed this time, we will continue to be an alternative in the future."

Later Monday, Mitzna and Labor legislators personally called undecided voters, working from a list of 15,000 names. "Hi, Sarah, it's Mitzna," the candidate began one conversation. Sarah turned out to be a civics teacher who was so uninspired by the campaign she decided not to vote at all. "No, no, Sarah, you can't disappoint me," Mitzna told her, and the brief talk ended with Sarah promising to reconsider.

Sharon spent most of the day at the prime minister's office. Later Monday, he was to call key Likud activists to make sure the party organization for Tuesday was in place.

Sharon has escaped blame for Israel's gloomy situation, with many voters convinced he inherited the mess from his predecessor, Ehud Barak of Labor. At a time of crisis, including a possible entanglement in a war with Iraq, Israelis are also not inclined to hand the reins to someone as politically inexperienced as Mitzna, currently the mayor of Haifa.

Many Israelis are also angry at the Palestinians, believing they responded to a reasonable peace offer with violence, and Israelis are not in the mood for compromise.

The Palestinians are resigned to a Sharon victory. "I think all indications are that things will get worse," said Palestinian Cabinet minister Saeb Erekat.

Palestinian leader Yasser Arafat has been careful not to endorse Mitzna, fearing such support would undermine the Labor leader's credibility among Israelis.

Arafat is closely following the vote because "it's an important issue ... for the entire region," said his adviser, Nabil Abu Rdeneh. The Palestinian leader expects "the Israeli right wing will win the election without any competition," the adviser said.