Responding to President Bush's (search) question with several of his own, Sen. John Kerry (search) said Monday he would have voted to authorize the war in Iraq knowing what he does now, but added that he would have used the power more effectively than the current commander in chief.

The Democratic presidential nominee said he hoped to begin reducing the number of U.S. forces in Iraq (search) within six months of taking office if he is elected. "It is an appropriate goal to have," he said, but added that achieving it would depend on broader international assistance, better stability within Iraq and other related factors.

Fielding questions from reporters after he and wife Teresa Heinz Kerry hiked along the rim of the Grand Canyon, Kerry also said he opposes raising the retirement age for Social Security (search) as part of any plan to overhaul the system.

"People who start talking about raising the retirement age are people who may not have worked at real jobs for a lifetime," he said.

Kerry, a Massachusetts senator, voted in October 2002 to give Bush authority for using military force to oust Iraqi leader Saddam Hussein.

At the same time, public opinion polls show that Bush's handling of the postwar period is unpopular, and the Democratic presidential nominee routinely accuses Bush of having sent troops into war without a plan to win the peace.

Last Friday, Bush challenged Kerry to answer yes-or-know to the question of whether he would have supported the invasion of Iraq "knowing what we know now" about the failure to find weapons of mass destruction (search).

"I have given my answer. We did the right thing and the world is better off for it," the president said.

In response, Kerry said, "Yes, I would have voted for the authority. I believe it was the right authority for a president to have."

Then he had a few barbed questions for Bush.

"Why did we rush to war without a plan to win the peace? Why did you rush to war on faulty intelligence and not do the hard work necessary to give America the truth?

"Why did he mislead America about how he would go to war. Why has he not brought other countries to the table in order to support American troops in the way they deserve it and relieve the pressure on the American people?"

Kerry faulted Bush for the use he made of the authority he had to wage war.

"American presidents should not send American forces into war without a plan to win the peace. This president did not have a plan to win the peace and the evidence is still that they are scrambling and struggling to try to find a way to do it," the Democrat said.

Specifically, Kerry noted that the administration is scrambling to persuade Arab countries to dispatch Muslim forces to Iraq. "All of this should have happened in the beginning," he said.

The presidential nominee said he intends "to get more people involved in that effort and I'm convinced I can be more successful than President Bush in succeeding in doing that."

Kerry said in an interview last week his goal was to begin reducing the number of troops in Iraq within the next year. Asked about his plans, he said he would use diplomacy to help build stronger international alliances.

The feasibility of that goal, he said, would hinge on "the stability of Iraq, the ability to have the elections, and the training and transformation of the Iraqi security force itself."

Kerry made his comments as he continued to campaign by train through several western battleground states -- Colorado, New Mexico, Arizona and Nevada, where he was scheduled to end his day.

He used the spectacular scenery of the Grand Canyon as the backdrop for an attack on the Bush administration's handling of the nation's parks. He said administration policies have resulted in a backlog of $600 million in underfunding, and promised to find the funds to erase it.

Asked where the money would come from, he said, "Tax cuts for the wealthiest Americans have to give." Kerry has proposed rolling back Bush-era tax cuts for the top 2 percent of American income earners, and using the funds for a variety of programs.

In addition, he said he may call for increased fees to raise money for the parks. He has said previously he favors changes in an 1872 federal mining law to increase the amount of money the government receives in royalties.