Americans should view the deadly attack on an Army helicopter in Iraq as the tragic but inevitable cost of waging a long war, Defense Secretary Donald H. Rumsfeld (search) said Sunday.

President Bush's Democratic rivals seized on the shootdown of the CH-47 Chinook transport helicopter (search), killing 16 soldiers and injuring 20, to press the administration to justify the mounting American death toll and to explain its strategy for getting out of Iraq (search).

The strike occurred as an ABC-Washington Post poll, for the first time, found that a majority of people surveyed -- 51 percent -- now disapprove of the way Bush is handling Iraq.

President Bush, who was at his Texas ranch Sunday, refused to personally comment on the attacks. He spent the day out of public view -- a "down" day between campaign appearances Saturday and Monday.

"We were misled into this conflict without a real strategy for success," former NATO commander Wesley Clark (search) told The Associated Press. Two other candidates, Rep. Dick Gephardt and Sen. John Edwards, said the United States needs more international help in making Iraq safe.

"We cannot solve this problem alone," Gephardt said on CBS' "Face the Nation," urging the president to sit down with foreign leaders, "treat them with respect and ... get the help that we should get from our friends."

Ohio Rep. Dennis Kucinich, the only candidate who voted against the resolution authorizing the war, said in a statement: "This disastrous mission must be ended before any more lives are lost. ... It is time to bring our troops home."

Rumsfeld said the strike underscores the difficulty of the military mission.

"In a long, hard war, we're going to have tragic days, as this is," he told ABC's "This Week." "But they're necessary. They're part of a war that's difficult and complicated."

The White House, reluctant to pull Bush into the politically perilous fray, initially let Rumsfeld do the responding in a series of TV appearances Sunday morning. Later, White House officials directed spokesman Trent Duffy to read a statement that reacted generically to continuing attacks on Americans.

Duffy declined to describe Bush's personal reaction to the helicopter downing, but said those killed "served the highest cause to defend freedom and protect Americans from dangerous new threats before they reach our shores."

Officials said the Chinook was carrying soldiers to Baghdad International Airport, where they were scheduled to catch flights out of the country for two weeks of vacation. The death toll initially was put at 15, but on Sunday evening a senior U.S. defense official in Washington said one among the original list of 21 injured had been declared killed in action, raising the death toll to 16.

Only two days earlier, the U.S. military announced it was expanding its R&R program, increasing from 270 to 479 the number of soldiers flown out of Iraq for rest and recuperation in the United States. The soldiers are flown to Baghdad from numerous collection points inside Iraq.

The strike highlighted the vulnerability of helicopters, especially the twin-rotor Chinook, a relatively large target with little means of defense against missiles.

The attack was the single deadliest event of the war for U.S. troops, which began in March and appeared all but over by May 1 when Bush declared the end to major combat operations.

Since then, at least 238 Americans have been killed in Iraq, mostly in small-scale attacks against troops on the ground.

Sunday's attack was the second time in just over a week that an Army helicopter was downed. A Black Hawk helicopter was hit with ground fire on Oct. 25 near Tikrit, a center of Iraq's anti-U.S. insurgency. No Americans were killed.

By targeting U.S. aircraft, the insurgents in Iraq stand a greater chance of killing sizable numbers of Americans in a single strike. They also take advantage of what Rumsfeld acknowledged was an enormous uncontrolled supply of surface-to-air missiles throughout the country.

There are "more than hundreds" of such missiles, Rumsfeld said. "There are weapon caches all over that country. They were using schools, hospitals, mosques to hide weapons." L. Paul Bremer, the American administrator of Iraq, said the missiles number in the thousands.

Bremer and others have said repeatedly that a key to defeating the Iraqi insurgency is obtaining better, more timely intelligence about threats against American troops and their Iraqi supporters.

Rumsfeld said it remains unclear whether Saddam Hussein, the deposed Iraqi leader, has had a hand in coordinating the resistance to U.S. forces. He acknowledged that as long as Saddam remains at large there will be Iraqis who fear he eventually will be restored to power.

"We will get him," Rumsfeld said on "Fox News Sunday."

"And I suspect he's still in the country. And I suspect he's having a great deal of difficulty operating. And we'll eventually find him."

Sen. Joseph Biden, D-Del., said that although expanding the U.S. military presence in Iraq may be "very, very unpopular" with the American public, he believes that more U.S. troops may be needed while an Iraqi security force is built up.

"And we have to be prepared to go back to our European friends and say, `We need more help. We're willing to give you more say in the formation of this government. We're willing to give you more impact here,"' Biden said on CBS' "Face the Nation."

Rumsfeld said that at this point there is no need for additional U.S. forces. The ultimate aim, he said, is to put the Iraqis in charge of their own security. To that end, about 100,000 Iraqis have been trained for security duties -- mainly police -- and the goal is to have about 200,000.

The ABC News-Washington Post poll released Sunday found that 51 percent of Americans disapprove of Bush's handling of Iraq, while 47 percent approved. His overall job approval in this poll was 56 percent.

The poll of 1,207 adults was taken Oct. 26-29 and has a margin of sampling error of plus or minus 3 percentage points, slightly larger for registered voters.