UNITED NATIONS - Bashing the United Nations seldom fails as an applause line for Republican presidential candidates.

Mitt Romney says the U.N. too often becomes a forum for tyrants when it should promote democracy and human rights. Newt Gingrich pledges to take on the U.N.'s "absurdities." Herman Cain says he would change some of its rules. Rick Perry says he would consider pulling the United States out of the U.N. altogether.

All that U.N. bashing has raised questions about whether a Republican victory could strain the relationship between the United Nations and its host country, the United States.

President Barack Obama's Democratic administration considers the U.N. critical to the country's interests, while Republicans traditionally have been disenchanted with the world body over America's inability to reliably win support for its positions. It doesn't help that U.N. members often criticize American policies, especially as they relate to Israel and the Palestinians.

That was reinforced last month when the U.N. cultural agency voted to approve a Palestinian bid for full membership in that body, and the U.S. responded by cutting off funding.

Yet history shows that any American president learns to get along with the United Nations "simply because there's a lot of stuff the U.N. does that is useful to the United States," said David Bosco, who writes the Multilateralist blog for Foreign Policy magazine.

Case in point: Even the harshest American critics were silent earlier this month when the U.N.'s nuclear watchdog concluded that Iran was probably developing nuclear arms.

Bosco, also an assistant professor at American University's School of International Service, noted that the Republican administration of George W. Bush supported a major expansion in U.N. peacekeeping despite regular sniping about the world body.

But the relationship wasn't a smooth one. Tensions ran high between the U.S. and the world body during the Bush presidency, especially when outspoken John Bolton was the U.S. ambassador.

U.N. officials have declined to comment on the possibility that a Republican win could strain the United Nations' relationship with the U.S.

"The United States is an important state at the United Nations and we would expect that relationship would continue under any administration," said Martin Nesirky, spokesman for U.N. Secretary-General Ban Ki-moon.

The presidential race has been dominated by the economy and other domestic issues, but foreign affairs are taking on greater importance and will be the subject of a debate by the Republican candidates Tuesday, giving them another chance to air their views on the U.N.

Cain said he has read and admires Bolton's foreign policy views, which are highly critical of the United Nations. But the former ambassador to the U.N. said Friday he has not endorsed any of the candidates.

One of the loudest U.N. critics among the candidates is Perry, the Texas governor who has recently slipped in the polls. "I think it's time for us to have a very serious discussion about defunding the United Nations," he declared in October.

Romney, a former Massachusetts governor, said in 2007 that U.N. failures were "simply astonishing," but he has been more measured during the current campaign.

U.N. supporters say that when the candidates bash the world organization, they are simply playing to the most conservative Republicans: the primary voters and caucus-goers needed early in the electoral contest.

"My sense is that if any of them were to be elected president, they would quickly realize that the U.N. serves American interests," said Peter Yeo, vice president for public policy of the U.N. Foundation, a nonprofit organization that supports the world body's work.

"They would find a way to constructively work within the U.N. system," Yeo added.

Detractors say that the candidates are just being truthful.

"I wouldn't call it U.N. bashing; I'd call it U.N. realism," said Bolton. "I think the issue for the United States is what to do to make the U.N. more effective, and the answer to that has to lie in how it is funded."

Contributions to the U.N.'s regular budget are assessed on a scale based primarily on a country's ability to pay. Additional contributions to U.N. entities such as the children's agency UNICEF are voluntary.

The U.S. assessment is the highest - 22 percent of the total U.N. operating budget. By comparison, China pays 3 percent.

In the 2010 budget year, the U.S. provided $7.7 billion to the U.N. for its regular budget, peacekeeping and other programs, up from $6.1 billion the previous year.

House Republicans recently introduced legislation to force the U.N. to adopt a voluntary funding system. The administration opposes it and it is unlikely to become law.