GAZA CITY, Gaza Strip – President Mahmoud Abbas on Friday vetoed Hamas’ plan to set up a security force of 4,000 militants, but Hamas insisted it would go ahead, deepening the bitterest clash yet between the Islamic group and the moderate Palestinian leader.

Hamas, which ousted Abbas’ Fatah Party from power in January parliamentary elections, had spoken in the past of incorporating militants into the Fatah-dominated Palestinian security forces.

But the concept of a shadow security force headed by the No. 2 fugitive on

Israel’s wanted list appeared to go too far for Abbas, who favors talks with Israel and is trying to keep the West from shunning the Palestinians over Hamas’ violently anti-Israel ideology.

The new force, to be based in chaotic Gaza, is to have about 4,000 members, or nearly one-fourth the size of the 18,000-member armed security contingent in the coastal strip.

Egypt, meanwhile, invited interim Israeli Prime Minister Ehud Olmert for an official visit even before he has put together his government, signaling it is eager to do business with a man keen to draw Israel’s final borders with the Palestinians within the next four years.

Egyptian President

Hosni Mubarak extended the invitation in a telephone call to Olmert, and a date for the visit is to be set next week, aides to the Israeli leader said. Israeli and Egyptian leaders haven’t met since February 2005.

Egypt’s MENA news agency reported the phone call, but did not mention any invitation.

Olmert has said he prefers a negotiated settlement with the Palestinians, but is expected to act unilaterally because of Hamas’ refusal to disarm or recognize Israel’s right to exist.

Hamas hard-line policies have already cost it hundreds of millions of dollars in Western aid and Israeli transfer payments. Abbas, who was elected separately, saw the proposed militants’ security force as yet another act of defiance, and on Friday, wielded his ultimate power — the presidential veto — to block the force.

“All the officers, soldiers and security personnel are asked not to abide by these decisions and to consider them null and void,” Abbas wrote in a letter to Prime Minister Ismail Haniyeh of Hamas. A text of the letter was obtained by The Associated Press.

Government spokesman Ghazi Hamad said Interior Minister Said Siyam, who nominally controls three of the six existing security forces, would form the new force as planned, despite Abbas’ veto.

“The decision of the interior minister conformed with the law … which gives the minister the authority to take the necessary decisions to guarantee security,” Hamad said. “The aim of the decision was to support and strengthen the efforts of the police, and not to replace the police.”

In

Syria, Hamas’ political chief, Khaled Mashaal, lashed out at Abbas’ veto, without mentioning the Palestinian leader by name.

“We can understand that Israel and America are persecuting us, and seeking ways to besiege and starve us, but what about the sons of our people who are plotting against us, who are following a studied plan to make us fai1?” Mashaal said.

Abbas’ clash with Hamas over the security forces is the bitterest tussle since the two sides started wrangling over authority.

Hamas’ proposed security force would draw its members from various militant factions. The force is to be headed by Jamal Abu Samhadana, 43, a founder of the small Popular Resistance Committees, which blew up three Israeli tanks in 2002 and 2003, killing seven Israeli soldiers. The group is also suspected in a deadly bombing attack on a U.S. diplomatic convoy in Gaza in 2003.

Abu Samhadana, who refused to discuss Abbas’ decree, told The AP he would continue his resistance despite his appointment to head the militants’ forces.

“I am not going to give up resistance,” he said. “There is no contradiction between the appointment and resistance. I am a fighter who is protecting the homeland.”

During five years of fighting, Israel has killed dozens of militants in targeted missile attacks. Abu Samhadana is high on Israel’s wanted list, and Israel has tried to kill him in targeted strikes.

“We have old scores to settle with this murderer,” Israeli Cabinet minister Zeev Boim told Israel Radio. “He has no immunity and we will have to settle this score sooner or later.”

Meanwhile, a senior Israeli military commander raised the pressure on Hamas by saying Israel is preparing for a possible invasion of Gaza.

Officials said there were no immediate plans to strike. But the comments reflected rising Israeli impatience with Hamas, which defended a suicide bombing in Tel Aviv this week and hasn’t halted militant rocket fire from Gaza.

“If the price we have to pay becomes unreasonable as a result of increased attacks, then we shall have to take all steps, including occupying the

Gaza Strip,” Maj. Gen. Yoav Galant, head of Israel’s southern command, told the Maariv daily. He said the plans have been approved by senior officials, including Defense Minister Shaul Mofaz.

Israel already has made two brief incursions into Gaza in recent days to search for explosives. But defense officials said the odds of a large-scale operation or full occupation are slim because of financial and political constraints.

Israel withdrew from Gaza last summer, ending 38 years of military occupation. Since the pullout, militants have fired rockets into southern Israel on nearly a daily basis.