MANCHESTER, N.H. (AP) - Sens. John McCain of Arizona and Sam Brownback of Kansas both admitted Tuesday night they voted to authorize the U.S. military invasion of Iraq without reading the formal National Intelligence Estimate in advance.

The confession drew a jab from former Gov. Jim Gilmore of Virginia in the opening moments of a presidential campaign debate. Members of Congress "ought to read at least that kind of material," he said.

Rep. Duncan Hunter of California said he had, the only member of Congress on the debate stage to make the claim.

The war dominated the opening moments of the debate, two nights after Democratic presidential hopefuls stood on the same stage at St. Anselm College in the nation's first primary state.

Both McCain and Brownback said they had received numerous briefings on the situation in Iraq before they cast their votes in 2002.

McCain said the invasion was the correct decision, arguing that international sanctions designed to prevent Saddam Hussein from developing weapons of mass destruction were breaking down.

He said the Iraqi dictator had used the weapons against his own people and "if he had gotten them again he'd have used them again."

Brownback also said he had received briefings on the issue. He went on to say he would propose legislation in the Senate on Wednesday to divide Iraq into three regions, controlled by the Sunnis, Shiites and Kurds.

National intelligence estimates are compilations of the best thinking of U.S. intelligence agencies, meant to provide the broadest guidance to government policymakers.

But they can be wrong. A 2002 assessment, for example, concluded that Iraq had continued its development of weapons of mass destruction, held arsenals of chemical and biological weapons and "probably will have a nuclear weapon during this decade."

McCain drew loud applause from the partisan debate audience when he turned a question about the war in Iraq into criticism of the leading Democratic presidential hopeful, Sen. Hillary Rodham Clinton of New York.

"When Senator Clinton says this is Mr. Bush's war, President Bush's war," she is wrong, he said. "When President Clinton was in power, I didn't say Bosnia was President Clinton's war," the Arizona senator said.

"Presidents don't lose wars. Political parties don't lose wars. Nations lose wars," he added.

The debate drew 10 Republican presidential contenders in all - but not former Sen. Fred Thompson of Tennessee, an actor apparently poised to join the race in a month's time.

"My name is Thompson. I'm the candidate, not the actor," said former Wisconsin Gov. Tommy Thompson in a jab at the man who wasn't there.

Controversial immigration legislation dominated the run-up to the debate.

"Do I think it's perfect? No. I would remind you the Democrats are in majority in both houses now and we have to deal with them to resolve this issue," McCain said in a campaign stop during the day.

McCain stands alone among GOP hopefuls in backing the bipartisan bill. The measure would tighten security on the Mexican border while allowing many of the 12 million illegal immigrants a chance to stay in the United States and eventually become citizens.

He has faced criticism from his rivals who oppose the measure, in particular Mitt Romney and Rep. Tom Tancredo, R-Colo., who contends the bill would grant amnesty to illegal aliens.

Also participating in the debate were former New York Mayor Rudy Giuliani, former Govs. Mike Huckabee of Arkansas and Ron Paul of Texas.

On Tuesday, Tancredo stood outside Republican Sen. Judd Gregg's New Hampshire office and said he would start a petition drive and volunteer network to help voters campaign against senators who support the White House-backed immigration plan.

"For a Republican to be talking about other Republicans, trying to take them on and defeat them in primaries, that's a somewhat injudicious thing for me to do. But this is an issue that surpasses all the niceties that go along with political camaraderie that you develop," Tancredo said.

Gregg has said he won't decide how to vote until he's seen all the details of the bill. He dismissed people who use "a jingoistic and demagogic approach of opposition to immigrants as a way to raise their own political visibility."

Romney has complained that a so-called Z visa included in the immigration legislation would allow the 12 million illegal immigrants already in the country to remain indefinitely, letting them jump ahead of other foreigners seeking to emigrate legally. He has proposed making the visas temporary, forcing recipients to seek permanent immigrant status or leave the country.

Nonetheless, one of his top economic advisers, N. Gregory Mankiw, former chairman of Bush's Council of Economic Advisers, signed an op-ed piece in Tuesday's Dallas Morning News supporting the bill.

"This is the most far-reaching and thoughtful reform of our immigration system in four decades and one that will significantly enhance American competitiveness," wrote Mankiw and his co-signers, including Jack Kemp, the 1996 Republican vice presidential nominee. "The benefits of the bill far outweigh its shortcomings. We believe it offers the only realistic way forward, and urge conservatives - and all Americans - to embrace the promise it holds out."

The debate was sponsored by CNN, WMUR-TV and the New Hampshire Union Leader. The host was Saint Anselm College, which also hosted a Democratic debate on Sunday.