There has been encouraging progress toward stabilizing Iraq, even while insurgents and foreign fighters "remain effective, adaptable and intent on carrying out attacks," Defense Secretary Donald H. Rumsfeld (search) said Wednesday.

Rumsfeld previewed a comprehensive Iraq (search) report to Congress that was due July 11, the first in a series of required periodic assessments. Lawmakers have been pressing the Pentagon to provide more specific data to measure progress.

Sen. Edward Kennedy, D-Mass., accused the Pentagon last week of delaying the report.

"It is unconscionable that the administration has failed to give the American people a straight answer about how many Iraqi security forces are adequately trained and equipped and able to defend Iraq's security on their own," he said.

Rumsfeld said information about the readiness and performance of U.S.-trained Iraqi security forces -- one of the most telling measures of progress -- would be included in a classified annex to the report but not made public.

"The information we're getting is in large measure from the Iraqi security forces," he said. "It's their information. It's not for us to tell the other side, the enemy, the terrorists, that this Iraqi unit has this capability and that Iraqi unit has this capability." He said it would be "mindless" to publish information about the combat readiness of Iraqi security forces that would reveal their strengths and weaknesses.

Speaking at the same news conference, Gen. Peter Pace (search), the vice chairman of the Joint Chiefs of Staff, said the Pentagon's unwillingness to release that information publicly does not mean Congress is kept in the dark.

"We do tell the Congress privately, classified, exactly what these facts are. So there is a dialogue, just not one in the public," Pace said.

Rumsfeld indicated Tuesday that the report, which he said would be provided to Congress on Thursday or Friday, would not include an estimate of how many U.S. troops are likely to be required in Iraq next year. That is among the things Congress had specifically requested be included in the unclassified report.

Rumsfeld said it is not possible to know how many U.S. troops will be needed because the size of the force will be determined by conditions, including further progress in containing the insurgency and training the Iraqis.

There currently are about 138,000 U.S. troops in Iraq, down from a peak of about 160,000 during the January elections, when extra units were required to handle a surge in violent attacks by the insurgents.

In describing the main points of the report to Congress, Rumsfeld highlighted signs of progress as well as problems.

"On the political front, terrorists have failed to derail the political process," he said. "A constitutional referendum remains on schedule for October 15th. And elections for a new assembly are scheduled for December 15th of this year."

He said ordinary Iraqis are growing more confident in their future, and there is progress on the economic and security fronts.

"The report also offers a candid assessment of the challenges that remain for the Iraqi people and for the coalition," he said. "Among them, though they've suffered numerous setbacks, terrorists in Iraq remain effective, adaptable and intent on carrying out attacks against Iraqi civilians and Iraqi officials.

"Extremists continue to try to foment tension, ethnic strife and, indeed, even civil war between Sunnis and Shias, through murder and attacks on religious sites." He also said Syria and Iran "remain notably unhelpful in assisting Iraq in securing its borders from foreign invaders."