The number of soldiers and Pentagon civilians who have died in Iraq topped the 1,000 mark yesterday, and Defense Secretary Donald H. Rumsfeld declared that the insurgency is likely to turn even more violent in coming months as the fledgling nation heads toward democratic elections.

By last night, military officials said, the death tally included 998 troops and three civilian employees of the Defense Department. The milestone came after a spate of deadly attacks over the past week by insurgents.

At a Pentagon news conference, Rumsfeld and Air Force Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, said suicide bombings and coordinated attacks were claiming more lives and displaying the insurgency's ability to frustrate the coalition with increasingly sophisticated tactics.

While offering that sober assessment, Rumsfeld was resolute when asked about reaching the 1,000-casualty mark, emphasizing the need to continue the fight against terrorism despite the sacrifices.

"When combined with U.S. losses in other theaters in the global war on terror, we have lost well more than a thousand already," Rumsfeld said. "And we certainly honor the courage and sacrifice of every man and woman in uniform who has served in Iraq and who is currently serving there."

The attacks over the past week reflect a determined opposition to U.S. and coalition forces that threatens to extend a war that U.S. officials once estimated would long be over by now. As U.S. forces work to build Iraqi security forces and support a new government, they find themselves still targets of an elusive and adaptive enemy.

"The enemy is becoming more sophisticated in its efforts to destabilize the country," Myers said.

Rumsfeld took the unusual step yesterday of saying that U.S. and coalition forces "probably" had killed between 1,500 and 2,500 former regime elements, criminals and terrorists last month. Pentagon officials generally have not been revealing enemy body counts, only occasionally offering estimates of enemy dead in specific incidents.

Rumsfeld's decision yesterday to provide an estimate for a full month was interpreted by some military analysts as a Bush administration effort to try to offset recent bad news from Iraq.

"They're grasping for good news," said Michael E. O'Hanlon, an expert on military affairs with the Brookings Institution. "They're in the situation where they needed something positive to say."

One reason Pentagon officials had avoided announcing body counts was concern that the figures were not reliable. They also have worried that people would focus on the numbers and compare them to estimates U.S. military authorities have given of insurgent forces. Last November, Gen. John P. Abizaid, who as head of the U.S. Central Command oversees American forces in the Persian Gulf region, pegged the size of the insurgency at about 5,000 fighters.

"The real issue is the fact that this enemy we have out there has the capacity to regenerate itself," said retired Army Gen. John Keane, who stepped down last year as the Army's vice chief of staff and recently visited Iraq. "It's doing so because of the disenfranchisement of a certain number of Muslims, the despair they feel in lack of quality of life improvement, and the sense of nationalism they also feel."

"The military can only provide a partial answer to that," Keane added. "The other answer has to be economic development and jobs."

According to the Pentagon's official tally, the 1,001 military and civilian casualties included 755 who were killed in action and 246 who died in such "non-hostile" situations as accidents and suicides. The number of wounded has totaled 6,916, including 3,076 who returned to duty.

After months of a steadily rising U.S. casualty count, crossing the 1,000 threshold has perhaps more symbolic significance at home than strategic impact on the battlefield. It drew immediate political response yesterday, and some predicted it would draw the American public's attention back to an Iraqi war that seemed sometimes overshadowed in the summer by political conventions and hurricanes.

"The 1,000-killed milestone will to lead an intensification of the focus on Iraq here at home," O'Hanlon said. "And that matters both for the fall election and also for Americans' willingness to stay the course."

Sen. John F. Kerry (D-Mass.), on the presidential campaign trail in the Midwest yesterday, called the 1,000 deaths in Iraq a "tragic milestone" for which the nation mourns.

"We must never forget the price they have paid," Kerry said. "And we must meet our sacred obligations to all our troops to do all we can to make the right decisions in Iraq so that we can bring them home as soon as possible."

Despite the rising death toll, Pentagon leaders made it clear yesterday that they do not intend to send U.S. troops to take over such embattled cities as Fallujah and Samarra, where it is believed extremists and terrorists are holed up and strengthening. While the U.S. forces have been engaging the enemy when attacked and hitting selected targets with airstrikes, they generally have stayed out of the strongholds.

Myers said yesterday that coalition forces plan to delay offensive moves in such cities until a full complement of Iraqi forces are trained and ready to defend their nation, something he said he believes can be accomplished by December. He said the "strategy for the cities" being developed by Army Gen. George W. Casey Jr. relies on working with the Iraqi government to send in joint forces.

"Part of that strategy is that Iraqi forces must be properly equipped, trained and led to participate in these security operations, and then once it's over, can sustain the peace in a given city," Myers said. "And while U.S. forces or coalition forces on their own can do just about anything they want to do, it makes a lot more sense that it be a sustained operation, one that can be sustained by Iraqi security forces."

This approach appears dictated by Iraqi political considerations.

"As I understand it, the reason why the U.S. has not gone in there to do anything more is because that's what the Iraqis want," Keane said. "There's no doubt that the Marines and the Army have the capacity to stop it. But the Iraqi leadership feels that the price may be too high, and what they really need is an Iraqi solution."

With national elections due in Iraq early next year, Keane said Iraqi authorities will need to go after the insurgent strongholds by then.

"I think you really have to clean things out before the elections and show the Iraqi people that you're not going to tolerate it -- so that they'll have some confidence in their government to protect them," he said.

Myers and Rumsfeld significantly scaled down the progress made in that direction, however, saying that 95,000 Iraqi forces are equipped and trained -- less than half the 200,000 forces U.S. officials had said they had already trained. They said they hope to reach 200,000 trained domestic soldiers in Iraq by mid-2005.

Joint Chiefs of Staff Chairman Richard B. Myers and Defense Secretary Donald H. Rumsfeld put enemy deaths at 1,500 to 2,500 last month.