WASHINGTON — Mayor Giuliani and Senator McCain are skipping the traditional Ames straw poll in Iowa this August, in moves that reflect the reality of a newly condensed primary calendar and potentially deal a death knell to what has been a key barometer of strength in the state that casts the first ballots in 2008.

Mr. Giuliani’s campaign announced its decision early yesterday, saying it wanted to save resources to spend competing in the actual binding caucus in January. Hours later, Mr. McCain’s campaign followed suit, reasoning that a victory in Ames would be rendered meaningless if Mr. Giuliani, who is leading the polls, was not competing.

The Arizona senator’s move offered Mr. Giuliani a large helping of political cover. Both campaigns sought to emphasize yesterday that they are committed to competing in the caucuses, but the candidates risk alienating Iowa voters, who take pride in the state’s tradition of holding the first primary contest.

The state Republican Party assailed the former mayor, saying he was “not taking Iowans seriously” by ignoring the August straw poll, which was first held in 1979.

“It’s exceedingly difficult to win on caucus night when you have missed the opportunity to speak to over a third of the caucus-goers at the largest gathering of Republicans in the nation,” the executive director of the Iowa Republican Party, Chuck Laudner, said in a statement.

After learning that Mr. McCain was joining Mr. Giuliani, a party spokeswoman, Mary Tiffany, said: “Obviously we’re just as disappointed that McCain is dropping out. But we also still feel confident that this event will be a success.”

Ms. Tiffany sought to downplay the notion that the absence of two leading contenders would make the poll irrelevant, saying Messrs. Giuliani and McCain would remain on the ballot and poll-goers could still vote for them.

The maneuvering yesterday left Mitt Romney as the top candidate committed to the poll, which takes place at a fund-raiser for the Iowa state GOP. His campaign tried to portray the withdrawal of Messrs. Giuliani and McCain as an early admission of defeat on their part.

“Our plan all along has been to play in the Iowa straw poll, and that hasn’t changed,” a campaign spokesman, Kevin Madden, said in a statement last night. “Campaigns that have decided to abandon Ames are likely doing so out of a recognition that their organizations are outmatched and their message falls flat with Republican voters in Iowa.”

Mr. Madden added: “It looks as if we just beat those campaigns in Iowa two months earlier than we had planned on beating them.”

The straw poll, which George W. Bush won in 1999 on his way to victory the next year, may be the first victim of the new, frontloaded primary calendar. More than 20 states, including New York and California, have moved their nominating elections to February 5, meaning campaigns will have to spread time and money across the country that might previously have been focused in the early voting states of Iowa and New Hampshire.

Mr. Giuliani’s campaign in particular has its eye on the larger states, where voters may not be as conservative as they are in Iowa.

His top aides acknowledged that the condensed calendar contributed to the decision, but they vowed to compete — and win — in Iowa in January.

“We are 100% committed to winning the Iowa caucuses in January,” Mr. Giuliani’s campaign manager, Michael DuHaime, told reporters in a conference call yesterday.

He said the campaign intended to take the estimated $3 million it would take to mobilize for the straw poll and spend it entirely for the January vote instead. Mr. DuHaime said he trusted Iowa voters not to hold the mayor’s decision against him.

“I don’t believe they’re going to base their decision on who went to a nonbinding straw poll in August,” he said.