JERUSALEM - The fighting in the Gaza Strip is laying bare a dangerous trend: Neither Hamas nor Fatah appears to be in control of its gunmen.

Furious over a two-month-old power-sharing deal and eager for a showdown, the groups' armed wings and their patrons - not the top political leaders - are calling the shots on the streets.

In a sign of their increasing weakness, Prime Minister Ismail Haniyeh of the Islamic extremist group Hamas and Palestinian Authority President Mahmoud Abbas of the largely secular Fatah movement failed to make a cease-fire stick despite repeated attempts this week.

At the root of the latest fighting, which has killed more than 50 and wounded dozens, is the failure of the Hamas-Fatah coalition deal forged in March to address the key issue of who controls Palestinian security forces. The government has also failed in its main task - bringing an end to an international aid boycott and leading the Palestinians out of isolation.

Discontent festered among Hamas hard-liners and in its military wing, which opposed the coalition deal from the start. In Fatah's armed wing, many also clamored for a showdown, having refused to accept the Hamas election victory last year that ended decades of Fatah domination.

The spark came last week when the top Abbas-allied security chiefs moved 3,000 security officers loyal to Fatah into the streets of Gaza City, ostensibly as part of a law-and-order crackdown.

Hamas, which demanded greater control over the security forces, perceived the deployment as a provocation and set off a deadly round of fighting Sunday by killing a top Fatah member.

Hamas and Fatah fighters appear about evenly matched, and fought to a draw in previous exchanges in the last year. Hamas, which commands roughly 20,000 armed men, has the better organization, while Fatah has more fighters, though an exact count is difficult.

In casting blame at the other, each side said the order to seek a confrontation did not come from its rival's leaders but from politically ambitious troublemakers and gunmen under their command.

"There is a mutiny" in Hamas, said Fatah spokesman Tawfiq Abu Khoussa. "The political leadership has no control over the military wing."

Hamas lawmaker Salah Bardawil accused Abbas security adviser Mohammed Dahlan, a Gaza strongman, of orchestrating a Fatah campaign against Hamas.

"The battle is clearly with [Dahlan and his allies] and not with Fatah as a whole," Bardawil said. "Even Abbas' control over them is limited."

During the clashes, Dahlan was in Cairo, Egypt, recovering from a knee operation. He has denied in the past that he is running his own agenda.

Both Hamas and Fatah clearly anticipated another round of violence. During the two-month lull after the power-sharing deal, they stockpiled weapons smuggled through tunnels under the Gaza-Egypt border.

In another sign of careful preparation, Hamas gunmen used computerized lists of pro-Fatah members of the security forces in roadblock checks, said Col. Ali Qaisi, a spokesman for the Abbas-allied Presidential Guard.

"This is a pure and naked power struggle," said Mouin Rabbani, an analyst with the International Crisis Group, an independent think tank.

The showdown has been further complicated by the involvement of Israel and the United States.

Israel has chased Hamas fighters out of their command centers with a barrage of air strikes, a response to Hamas rocket fire at the southern Israeli town of Sderot. The Israelis also let 500 Fatah fighters trained in Egypt cross into Gaza on Tuesday.

Israel insists it has no plan to get into the middle of the Gaza power struggle, but its targeting of Hamas has helped Fatah fighters.

The United States, meanwhile, has arranged for training and financial support for Abbas' Presidential Guard, which is supposed to deploy men at Gaza's border crossings and in antirocket units as part of a U.S. security plan.

This has given ammunition to Hamas' claims that Fatah is conspiring with outsiders. Hamas TV yesterday accused three Fatah security chiefs of treason, alleging they were in contact with foreign security services.