President-elect Barack Obama will inherit a perilous situation in the Middle East, with Israel under increasing pressure to halt its ground invasion of the Gaza Strip, key Arab leaders close to the United States greatly weakened and the Hamas militant group earning resurgent popularity in the region.

After days of studied silence on the Gaza conflict, Obama promised yesterday "to hit the ground running" on achieving a broad Middle East peace deal.

"We are going to engage effectively and consistently in trying to resolve the conflicts that exist in the Middle East," he told reporters, adding that "the loss of civilian life in Gaza and Israel is a source of deep concern to me, and after January 20th I am going to have plenty to say about the issue."

Secretary of State Condoleezza Rice traveled to the United Nations yesterday to meet with Arab and European diplomats on possible terms of a truce, pressing the Bush administration's case that a cease-fire must be permanent and not grant Hamas the ability to rebuild its military arsenal. There is little indication that Obama and his team differ significantly from that approach.

One of Obama's biggest challenges will be to craft diplomatic solutions that do not have unintended consequences. Good intentions go only so far in the Middle East, and today's battles often can be traced to choices made by the Israeli government or the Bush administration that ended up backfiring.

In the 1980s, for instance, the Israeli government decided to weaken the secular Fatah movement headed by Palestine Liberation Organization Chairman Yasser Arafat by promoting the rise of Islamic parties as a counterweight, on the theory that Islamic groups would not have the same nationalistic impulses.

So Fatah's social networks were dismantled by the Israeli government, but it went easy on Islamic charitable networks. This decision fueled the rise of Hamas as a political force, with its network of health clinics and social services that far exceeded the abilities of the often-corrupt Fatah movement.

"There's no question there was a degree of blowback," Aaron David Miller, a former Middle East negotiator and the author of "The Much Too Promised Land."

Israel now wants to make a peace deal with Mahmoud Abbas, the Palestinian Authority president who heads Fatah but has no control over Gaza. So one of the Israeli aims in Gaza today is to weaken Hamas enough that it no longer can be a political rival to Fatah in Gaza -- precisely the opposite of what Israel hoped to achieve decades ago with its efforts to encourage the rise of Islamic groups.

"This is not like a regime-change operation, but at the end of the day, the restoration of the Palestinian Authority back to Gaza should be on the agenda as a whole," said Jeremy Issacharoff, deputy chief of mission at the Israeli Embassy in Washington.

Similarly, the Bush administration encouraged Israel to withdraw from Gaza and demolish its settlements there, arguing that it was a step forward on peace. But, as a condition, then-Israeli Prime Minister Ariel Sharon in 2004 demanded a letter from President Bush in which the United States conceded two critical peace issues on settlements and refugees to Israel. The Israeli government later cited the letter as giving implicit permission to continue some settlement expansion during peace talks brokered late in the Bush administration, undermining those efforts.

The Bush administration also did not effectively push Israel to negotiate its 2005 withdrawal from Gaza with Abbas, who had just been elected president after Arafat died. Abbas wanted to demonstrate that he could negotiate with the Israelis, but Jerusalem withdrew from Gaza unilaterally, as had been the plan when Arafat was still alive.

Ghaith al-Omari, a former top Abbas aide, remembers bitterly that Hamas strung up a huge banner after Israeli troops departed: "Three Years of Intifada Beat Ten Years of Negotiations."

"Hamas took all the credit for the withdrawal," Omari said. "It was a clear strategic mistake."

Then the United States pushed for legislative elections in the Palestinian territories in early 2006, hoping for a demonstration of democracy on the march in the Middle East. The Israelis tried to sound a warning about including Hamas on the election list. In October 2005, then-Justice Minister Tzipi Livni (now foreign minister) flew to Washington to plead that Hamas not be permitted to run, only to be told by U.S. officials: "Don't worry, Hamas won't win."

Hamas defeated Fatah, instantly elevating its status and spawning the crisis that led to today's conflict. Hamas eventually took over all of Gaza, giving it the ability to terrorize Israeli cities with increasingly sophisticated rockets.

Now, some experts say, the seeds of more conflict will be planted without careful diplomacy by the incoming U.S. administration. Abbas, who was at the United Nations yesterday pleading for an immediate cease-fire, had seen his popularity rise in recent months, but the Israeli invasion has once again turned Hamas into Arab heroes. Arab leaders in Egypt, Jordan and Saudi Arabia -- who hold no fondness for Hamas -- face growing pressure at home to condemn Israel as Palestinian deaths climb.

"The Gaza crisis has weakened all those on the Arab side who would be Obama's partners," said Martin Indyk, author of "Innocent Abroad," a just-published memoir of serving as a peace negotiator in the Clinton administration. "Obama will have to mobilize Arab leaders in support of a major effort" to resolve the conflict. Otherwise, he said, groups such as Hamas -- who are threatened by Obama's popularity in the Arab world -- "will brand him as the same as George Bush."

To avoid previous pitfalls, Indyk said, "you have to stay flexible. You cannot know how the actions of the superpower will affect the leaders of the region. You push on one door -- and another door will open."