BAGHDAD, Iraq - Defense Secretary Donald H. Rumsfeld said Wednesday that political reconciliation between Sunnis and Shiites is as important as the military effort in establishing security in Iraq, where thousands more U.S. troops have been summoned to Baghdad to quell an upsurge in violence.

The U.S. may have to send still more troops to the capital city, said the top U.S. general in the country, while Rumsfeld said it was too early to estimate when overall levels of U.S. forces in Iraq might begin to fall.

Gen. George Casey, the senior U.S. commander, said al-Qaida has increased its killings in Baghdad to show it remains a force to be reckoned with after the June 7 killing of its leader in Iraq, Abu Musab al-Zarqawi.

In response to the al-Qaida attacks, "what we are seeing now as a counter to that is death squads, primarily from Shiite extremist groups that are retaliating against civilians," Casey said at a news conference with Rumsfeld. "So you have both sides now attacking civilians, and that is what has caused the recent spike in violence here in Baghdad."

Casey said he was consulting with the Iraqi government on how to counteract the violence. Asked whether that might include putting more U.S. troops in the Baghdad area, Casey replied, "It may, yes."

"We'll make sure there are adequate forces available for the Iraqis to succeed in Baghdad," he added. Rumsfeld said earlier Wednesday that the number of Iraqi and U.S. troops in Baghdad had recently grown from 40,000 to about 55,000.

Overall, there are about 129,000 U.S. troops in Iraq.

Rumsfeld said U.S. forces remain committed to helping stabilize the country, but he stressed that the key concern now is political rather than military.

"It's as much a political task as anything," he told reporters who were accompanying him on his 12th visit to Iraq since the March 2003 invasion that toppled Saddam Hussein and his Sunni Arab powerbase. "They're going to have to engage in a reconciliation process" between Sunnis and Shiites, including the Shiite militias that are engaging in acts of intimidation and violence in the Baghdad area, Rumsfeld said.

In the latest violence Wednesday, Iraqi authorities said gunmen ambushed a bus station in a town northeast of Baghdad, in a province where sectarian tensions run high, kidnapping two dozen people and killing all but four of them.

Rumsfeld met with Prime Minister Nouri al-Maliki and members of his Cabinet, who are under growing pressure to show better results from a monthlong crackdown on violence in the capital. Al-Maliki was scheduled to appear at a news conference with Rumsfeld, but Defense Minister Abdul-Qader Mohammed Jassim al-Mifarji attended in his place.

Rumsfeld said earlier Wednesday that the Iraqi government is not yet ready to decide on security issues that will determine the pace of U.S. troop reductions this year.

Speaking to reporters on a flight from southern Afghanistan to an air base at Balad, Iraq, Rumsfeld said the Iraqis are embarked "on a comprehensive review" of their security requirements.

Asked how long that might take, he said, "I don't talk deadlines."

U.S. officials have expressed hope that U.S. troop strength could be reduced to 100,000 by the end of the year, with further cuts in 2007. Rumsfeld's remarks suggested that the timing and the scope of troop cuts were still in doubt.

Rumsfeld also indicated on his flight to Iraq that he did not expect any change for now in the legal arrangement under which American troops fighting in Iraq are immune from domestic laws. Some Iraqi leaders have questioned that immunity in light of a recent string of allegations of murder and other atrocities by U.S. troops against Iraqi civilians.

He said the allegations, "It's being handled as it should be."

He indicated no heightened level of concern about the conduct of U.S. troops and said he did not intend to raise the matter in his talks Wednesday with top commanders.

Rumsfeld held a town hall style meeting with troops at the air base at Balad, a major logistics hub for the distribution of supplies to troops throughout Iraq. He offered his audience of several hundred troops a definition of "what victory means."

"First and foremost it means helping the Iraqi people take the fight to the enemy," he said. He described the enemy in Iraq as "persistent and ruthless," even after a series of tactical defeats and the loss of al-Zarqawi, the terrorist leader who was killed in a U.S. airstrike in early June.

"These enemies are not going to quit," he said.