President Bush and leading Republicans are increasingly charging that Democratic presidential nominee John F. Kerry and others in his party are giving comfort to terrorists and undermining the war in Iraq -- a line of attack that tests the conventional bounds of political rhetoric.

Appearing in the Rose Garden yesterday with Iraq's interim prime minister, Ayad Allawi, Bush said Kerry's statements about Iraq "can embolden an enemy." After Kerry criticized Allawi's speech to Congress, Vice President Cheney tore into the Democratic nominee, calling him "destructive" to the effort in Iraq and the struggle against terrorism.

It was the latest instance in which prominent Republicans have said that Democrats are helping the enemy or that al Qaeda, Iraqi insurgents and other enemies of the United States are backing Kerry and the Democrats. Such accusations are not new to American politics, but the GOP's line of attack this year has been pervasive and high-level.

* On Tuesday, Sen. Orrin G. Hatch (R-Utah), chairman of the Judiciary Committee, said terrorists "are going to throw everything they can between now and the election to try and elect Kerry." On Fox News, Hatch said Democrats are "consistently saying things that I think undermine our young men and women who are serving over there."

* On Sunday, GOP Senate candidate John Thune of South Dakota said of his opponent, Senate Minority Leader Thomas A. Daschle: "His words embolden the enemy." Thune, on NBC's "Meet the Press," declined to disavow a statement by the Republican Party chairman in his state saying Daschle had brought "comfort to America's enemies."

* On Saturday, House Speaker J. Dennis Hastert (Ill.) said at a GOP fundraiser: "I don't have data or intelligence to tell me one thing or another, [but] I would think they would be more apt to go [for] somebody who would file a lawsuit with the World Court or something rather than respond with troops." Asked whether he believed al Qaeda would be more successful under a Kerry presidency, Hastert said: "That's my opinion, yes."

* The previous day in Warsaw, Deputy Secretary of State Richard L. Armitage said terrorists in Iraq "are trying to influence the election against President Bush."

Such accusations have been a component of American politics since the Alien and Sedition Acts of 1798 and surfaced in the modern era during the McCarthy communist hunt and the Vietnam War protests.

"Rhetoric this sharp and ugly is not by any means brand-new," said Jeff Shesol, a speechwriter for President Bill Clinton and author of a book about Lyndon B. Johnson and Robert F. Kennedy. "What we're seeing now isn't just offhand comments by outliers but clearly a decision by the Republican hierarchy to put this charge out there consistently."

Pollster Frank Luntz, who has advised Republicans on rhetoric, cautions that "statements like that can cause a backlash" against the accuser. "Candidates have to be careful of going over the line," he said.

Earlier this month, Cheney provoked an uproar when he said that on Election Day, "if we make the wrong choice, then the danger is that we'll get hit again, that we'll be hit in a way that will be devastating" and that the United States would not respond vigorously. Cheney later said that he was not suggesting the country would be attacked if Kerry were elected. But a few days later, he said: "We've gone on the offense in the war on terror -- and the president's opponent, Senator Kerry, doesn't seem to approve."

The White House and the Bush campaign said they would neither endorse nor disavow the remarks by Hastert, Armitage and others. "Those statements speak to the great concern many people have about John Kerry's consistent vacillation under political pressure on the most significant issues the nation faces with regard to the war on terror," Bush campaign spokesman Steve Schmidt said.

White House press secretary Scott McClellan had no quarrel with the remarks. "They are expressing their opinion," he said.

The Kerry campaign, which previously branded Cheney's accusations "un-American," extended that complaint to Bush's remarks yesterday.

"Not only is it un-American, it's un-democratic the way they attack your patriotism when you tell the truth about Iraq," Kerry campaign spokesman Chad Clanton said. "It's called an election, and people deserve an honest debate."

Responding to Hastert and Cheney's remarks, House Minority Leader Nancy Pelosi (Calif.) said yesterday: "These despicable comments cross the line from partisan politics to shameless fear tactics. . . . Republicans should remember that the reason Osama bin Laden is still able to threaten the United States three years after the September 11th attacks is the utter failure of the Bush administration to catch him and destroy al Qaeda."

Such charges surfaced soon after the attacks on Sept. 11, 2001. Late that year, Attorney General John D. Ashcroft said tactics used by critics of the USA Patriot Act "only aid terrorists" and "give ammunition to America's enemies." In 2002, Bush charged that opponents of his version of homeland security legislation are "not interested in the security of the American people." In 2003, Defense Secretary Donald H. Rumsfeld said that if terrorists think Bush's opponents might prevail, "they take heart in that, and that leads to more money going into these activities or that leads to more recruits or that leads to more encouragement."

This year, the accusations began at lower levels. In March, Rep. Tom Cole (R-Okla.) told a group of Republicans: "If George Bush loses the election, Osama bin Laden wins the election." Republicans say Democrats, while not suggesting Bush is guilty of treason, have indulged in questionable rhetoric themselves; they point to a tasteless performance at a Kerry fundraiser by performer Whoopi Goldberg (which the candidate did not disavow) and by Rep. Jim McDermott (Wash.), who on a visit to Baghdad two years ago defended Iraq and said Bush was misleading the public.

On Fox News, conservative commentator Ann Coulter said, "It's unquestionable that Republicans are more likely to prevent the next attack." Kerry, she said, "will improve the economy in the emergency services and body bag industry."

Whatever the merits, the charges that terrorists prefer Democrats have been echoed by independent commentators and journalists. CNN analyst Bill Schneider, asked about Hastert's remarks, agreed that al Qaeda "would very much like to defeat President Bush."