Yassin's wife, Halima, greeted mourners at their modest Gaza City home. "We're counting on God and God will give us our revenge ... on the Jews I hope, and on the collaborators, and on the spies," she said. The couple had 11 children.

The Palestinian Authority declared three days of mourning and stores throughout the West Bank and Gaza Strip were closed. Hamas is the biggest rival to the authority, but Palestinian leaders treat the movement with care because of its popularity.

Israeli security chiefs are closely watching to see who fills the political vacuum caused by Yassin's death. At least initially, hardliner Abdel Aziz Rantisi, has emerged as a Hamas strongman. Rantisi, a 54-year-old pediatrician who escaped an Israeli assassination attempt last June, opposes even a temporary truce with Israel.

Ismail Hanieh, a top Yassin aide, said Hamas took a blow to morale, but would continue carrying out attacks on Israel. "Sheik Yassin's death is not going to harm or affect the movement. It's going to give us encouragement to go ahead with our program to achieve our goal," Hanieh said.

However, Israel has become more effective in preventing attacks. The number of suicide bombings and the number of victims has dropped, with 142 Israelis killed in 22 bombings in 2003, compared to 214 killed in 53 bombings in 2002.

Analysts attributed the drop to Israel's partially built West Bank barrier, its beefed up intelligence, a brief cease-fire in 2003 and Hamas leaders' fears of assassination.

In the meantime, Israel has increased security both at home and abroad. Jerusalem's usually lively streets were mostly empty Monday night, due to fears of a Hamas attack. Buses remained empty on Tuesday.

Checkpoints were set up around major cities, and police were visible on city streets Tuesday. Tel Aviv police commander Yossi Sedbon told Army Radio that he expects the alert level to remain high for at least a month.

A closure preventing Palestinians from entering Israel from the West Bank and Gaza remained in effect, and the army increased forces throughout the Palestinian areas, officials said. Five Palestinians died in violence following Yassin's killing Monday; sporadic stone-throwing clashes in the West Bank were reported Tuesday.

Troops prepared for a variety of scenarios, including kidnappings and attacks on army bases and Jewish settlements in the West Bank and Gaza, the officials said. Security also was beefed up for military and political leaders.