Anticipating an increase in insurgent attacks, the United States plans to send more troops to Iraq in advance of an Oct. 15 referendum on a new Iraqi constitution, which is considered unlikely to halt the country's violence, Defense Secretary Donald H. Rumsfeld said today.

In a Pentagon news conference, Rumsfeld dismissed the notion that the constitution, which was submitted to the Iraqi parliament late Monday but not immediately put to a vote, would trigger a civil war, as some prominent Sunni Muslim opponents have warned.

But he also cautioned that the charter would not be a panacea for Iraq's ills, and he said insurgents were likely to ramp up their attacks ahead of the scheduled ratification vote, following a pattern in which surges of violence have coincided with major events on Iraq's path to democratic self-rule.

The Iraqi constitution was submitted to parliament minutes before a midnight Monday deadline, but the parliamentary speaker postponed a vote on it for three days to give negotiators more time to secure agreement from Sunnis who were outraged by some of its provisions. The draft constitution is strongly backed by Iraq's majority Shiite Muslims and the Kurdish ethnic minority, two groups that were long suppressed under the rule of former president Saddam Hussein, but who now have the numbers in parliament to pass the constitution easily over Sunni objections. The insurgency is based chiefly in Sunni areas, and U.S. officials have strongly promoted a new constitution as a way to separate the insurgents from the Sunni population.

After approval by the National Assembly, or parliament, the constitution must be put to a vote by the public in the referendum scheduled for October. Elections for a new government under the charter are scheduled for December.

The constitution-writing process "has been delayed a bit, but democracy has never been described as speedy, efficient or perfect," Rumsfeld told reporters today. "And regrettably, completing the constitution is not likely to end all the violence in Iraq or solve all of the country's problems. But it will represent one more important step toward cementing a new way of life for Iraqis, one ruled by ballot boxes rather than by death squads."

Appearing before reporters with the newly named vice chairman of the joint chiefs of staff, Adm. Edmund Giambastiani, Rumsfeld denounced people who he said predict U.S. failure in Iraq.

"So those being tossed about by the winds of concern should recall that Americans are a tough lot and will see their commitments through," he said.

He rejected the idea that American troops risk being caught up in a civil war over the constitution. "Just the opposite's been happening," he said. "People have been moving together, talking, discussing things."

"It hasn't happened yet," he said of the prospect of civil war. "It is not happening now. And, obviously, it is something that one has to be attentive to and be concerned about. But I haven't seen anything to indicate that the risk is greater today than it was yesterday or the day before."

Asked whether, in view of growing public opposition to the war, the U.S. war effort can be sustained, Rumsfeld said, "I think it'll have the support of the American people, and it will be sustained, and we will be successful." The alternative, he said, would be to turn Iraq over to terrorists. "That would be to turn to darkness," he said.

Rumsfeld also dismissed the view of Republican Sen. Chuck Hagel of Nebraska, a Vietnam veteran who compared the situation in Iraq to the Vietnam war.

"The differences are so notable that it would take too long to list them," Rumsfeld said without elaborating.

Rumsfeld said he did not know how to explain an increase in U.S. casualties in Iraq from roadside bombs, "other than the fact that they [insurgents] obviously are becoming more sophisticated in developing, in large measure, explosive devices which have greater lethality."

But he said that while some roadside bombs have been deadlier, the "overwhelming majority" of them -- about 75 percent -- "are not effective at all" and cause no casualties.

Rumsfeld noted that the United States has increased its troop presence in Iraq and Afghanistan in the past around the time of elections.

"And we very likely will be announcing a temporary increase in forces in Iraq in anticipation of the October 15th" referendum, he said. The increase in U.S. forces would be on the order of 1,000 to 2,000, he said. "A couple of battalions," Giambastiani added.

Asked about the recent comments of Rev. Pat Robertson, a conservative Christian broadcaster who called for the assassination of leftist Venezuelan President Hugo Chavez, Rumsfeld said such an action would be "against the law" and that "our department doesn't do that type of thing." Robertson, a supporter of President Bush and founder of the Christian Coalition, is "a private citizen," Rumsfeld said. "Private citizens say all kinds of things all the time."