Ismail Haniya played down the rivalry with the PA
They spoke in Gaza only two days before Israel is due to start pulling settlers and troops out of the territory.
The group has largely kept to a truce with Israel called in February by the Palestinian Authority's president.
But it has defied Mahmoud Abbas' calls to disarm in preparation for Israel's withdrawal and the transfer of power.
Palestinian security forces were deployed around the Gaza settlements on Saturday to positions not occupied since the intifada erupted nearly five years ago, in preparation for the withdrawal, Palestinian sources told AFP news agency.
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Inside the settlements all was reported to be quiet on Saturday's Sabbath.
On Monday those who have not yet left will be asked by Israeli soldiers to depart. If they refuse they are expected to be dragged away.
A BBC correspondent says thousands of protesters have made it into the settlements to prepare for the confrontation.
Saturday's gathering of Hamas leaders was the biggest in public for more than a decade.
One of them, Ismail Haniya, was surrounded by four founding members of the group as he addressed reporters in a restaurant in Gaza City.
"Hamas confirms it is committed to armed resistance, it is our strategic choice until the end of the occupation of our land," he said.
"Our land, including Jerusalem, is still occupied, the refugees are still deported, the wall and the settlements are still eating more of our land."
Defiance
The Hamas leaders positioned themselves in front of their green flag and draped themselves in the group's colour, defying Palestinian Authority (PA) officials, who said on Friday that only the red, black, green and white Palestinian banner should be used to celebrate Israel's withdrawal.
The PA organised a rally of fishing boats
On Friday the PA organised a fishing boat rally in the harbour of Gaza City to celebrate the imminent pullout, where Mr Abbas told crowds that Palestinians were on the path to an independent state.
Tensions between the PA - dominated by Mr Abbas' Fatah party - and Hamas are high in the run-up to withdrawal, for which both claim the credit.
Hamas is planning to run in parliamentary elections in January.
Last month clashes broke out when Palestinian security forces tried to prevent Hamas members firing rockets at Israeli settlements in Gaza.
Mr Haniya played down the rivalry, but made clear Hamas intended to take part in governance after the withdrawal.
"Hamas is not a replacement for anyone. It is not a power within the Palestinian Authority and it is not confronting it. But Hamas rejects the idea of allowing any party to monopolise decision-making process," the Hamas leader said.
Palestinian flag
During overnight raids, Israeli soldiers arrested 10 people, allegedly members of Islamic Jihad, a Palestinian militant group. The raids were conducted during two operations near the towns of Jenin and Nablus. An M-16 rifle was also discovered during the raid near Jenin.

Meanwhile, Hamas, a group friendly to Islamic Jihad, made a rare public appearance 2 days before the Israeli pull-out of settlers and troops from The Gaza Strip. They defied the Palestinian Authority by draping themselves in the colours of the group. On Friday, Palestinian Authority officials said only the Palestinian banner of red, black, green and white should be used to celebrate the withdrawal of Israel from Palestinian territory.

Hamas are planning to run in the parliamentary elections to be held in January, next year.