STANHOPE, Iowa — Lambasting Democrats for having “embraced defeat” in Iraq, Mayor Giuliani is declaring himself the only Republican who will keep America “on the offense” against extremist Islam and stop Senator Clinton from capturing the White House in 2008.

“I think it’s going to be a Hillary Clinton-Barack Obama ticket,” he said during a campaign stop at Sparky’s One Stop, a gas station in the village of Stanhope — population 488 — in rural Iowa.

“They will run together because Barack Obama has had such a good showing, and it’s going to be very hard for her to deny him a place on the ticket.”

But although many Democrats view such a “dream ticket” of the aspiring first female president and the first black vice president as unbeatable, Mr. Giuliani predicted he could beat them.

“Every poll says I am the Republican who has the best chance of winning against any of the Democrats,” he said. “We’re going to need the strongest possible Republican who can win in every state, and I’m the only one who can do that.”

Mr. Giuliani leads the field of Republican contenders for the presidential nomination despite his liberal positions on abortion, gun control, and gay marriage. Although Democrats enjoy a huge lead as a party over Republicans in national opinion polls, Mrs. Clinton is only about five percentage points ahead of the former mayor when voters are asked who they would prefer as president.

Polls also show most Americans favor an Iraq pullout. But a majority of Republican primary voters back President Bush’s troop surge, and Mr. Giuliani is calculating that even those in the wider electorate who are against the Iraq war are not yet prepared to accept defeat as inevitable.

Democrats would lose in 2008, Mr. Giuliani told a crowd of about 60, because they wanted to capitulate to America’s enemies. “The leading Democrats are preaching defeat in Iraq. In fact, they’ve embraced defeat. About a month ago, they decided we’ve got to pull out of Iraq. Even if you want an army to retreat — which I don’t think they should — when have you ever heard in the history of war of giving the enemy a timetable of retreat?” Although he railed against Democratic plans for “socialized medicine” and “big, big government” and high taxes, his persistent theme was that he had proved that he would confront terrorism. “We don’t need that kind of [Democratic] leadership for America. That’s leadership that gives us a self-fulfilling prophecy of loss. America doesn’t lose, America advances.”

Mr. Giuliani said his centrism on social issues made him competitive with Democrats across the country, while for Republicans, winning the war on terror trumped everything.

“If you want to defeat Hillary Clinton, I would be the best person to do that because I can make this campaign nationwide. We can build it to … have a good chance of winning in New York and in New England and in California and Oregon — these are states where Republicans haven’t even had a campaign for a long time.”

For voters, “if there is a single issue in this campaign, it’s who is going to deal most effectively with Islamic terrorism. And the other issues kind of work their way in.” His executive experience, he said, also gave him the edge over the Democratic candidates. “They haven’t run a city, a state, or a business. I’ve run a city that’s the size of a state and a business.”

Could Mr. Giuliani win? Stanhope’s deputy sheriff, Paul Whitmore, was doubtful. “President Hillary Clinton? That’s a scary thought. I believe it’s a rightful war in Iraq, but it’s hurt Republicans. It’s going to be darn tough for us.”