KETZIOT PRISON, Israel — Dozens of Palestinian prisoners at this desert jail removed their brown prison jumpsuits, donned civilian clothes and left for home today as Israel freed them in a move meant to bolster President Abbas of the Palestinian Authority.

But as the prisoners headed home, Israel said it was moving forward with plans to open a new West Bank police headquarters, despite American concerns that development in the area harms prospects for establishing a viable Palestinian Arab state. The Palestinian Arabs accused Israel of undermining new peace efforts.

Israel was freeing a total of 87 prisoners. Two buses carrying 57 prisoners to the West Bank left Ketziot around midday, while the release of 30 additional prisoners to the Gaza Strip was delayed. Israel’s Prisons Authority gave no reason for the holdup.

Most of the prisoners are from the West Bank, which is controlled by Mr. Abbas and his government of moderates. The others are residents of Gaza, which has been ruled by Hamas since June, when they defeated the forces of Mr. Abbas’ Fatah movement and took control of the coastal territory.

Prime Minister Olmert announced the prisoner release — the second since July — last month as part of his strategy to support Mr. Abbas in his power struggle with Hamas. The prisoners are mostly members of Fatah, along with several who belong to smaller Palestinian Arab factions. None belong to Hamas.

Israel is holding around 11,000 Palestinian Arab prisoners, and their release is a central Palestinian Arab demand. While many of those released today were serving time for militant activity, none was convicted in attacks on Israelis.

In Gaza City, group of Palestinian Arabs with relatives in Israeli prisons gathered at the Red Cross offices, holding photographs of their imprisoned loved ones.

One mother, Fatima Kaisi, said her 24-year-old son Mohammed is serving a 250-year sentence for his involvement in the radical militant group Islamic Jihad.

“I’m happy for the mothers who are getting their sons back today, but the leaders have to know that there are hundreds of mothers and families still waiting to meet with their loved ones,” Ms. Kaisi said.

In Gaza, Israeli troops killed two Hamas militants today in a nighttime gunbattle, Hamas announced. The Israeli military said troops shot two armed Palestinian Arab militants who attacked troops inside Gaza not far from the Israeli border. One soldier was lightly wounded by gunfire, the military said.

As Israeli keeps up its military pressure on militants in Gaza, Mr. Olmert is slated to meet with Mr. Abbas on Wednesday. The two leaders are attempting to draft a joint vision of a peace deal that will be presented at a peace conference expected to be held in November in Annapolis, Maryland.