But the high-profile disputes, mainly over policies in Iraq, mask what continues to be close engagement between both sides. That will likely be stressed during UN Secretary-General Kofi Annan's visit to Washington on today.
Annan is expected to address the relationship in a speech to the Council on Foreign Relations. He is also due to hold separate meetings with Secretary of State Colin Powell and his designated successor, Condoleezza Rice, on issues including the Iraqi elections, Afghanistan, Sudan, and Haiti.
On the eve of his trip, Annan brightened the mood by announcing plans to expand the presence of UN experts to the Iraqi cities of Irbil and Al-Basrah. John Danforth, the U.S. ambassador to the UN, praised the move following talks with Annan. "I think the UN understands the importance of the election [in Iraq], understands the importance of UN support for the election and feels that that support is going to be forthcoming," Danforth said.
The limited UN presence in Iraq, due to security concerns, has been an irritant for Washington, which considers the 30 January polls key to Iraq's stability.
Separately, there have been calls by some Republican members of the U.S. House of Representatives for Annan to resign over corruption scandals in the UN's oil-for-food program in Iraq.
The administration has distanced itself from those calls while asserting the importance of an ongoing independent investigation into claims that the UN allowed former Iraqi leader Saddam Hussein to defraud the program.
However, this week Washington made clear its opposition to a third term for Muhammad el-Baradei, director-general of the International Atomic Energy Agency (IAEA).
In public statements, U.S. officials have cited an agreement that limits the IAEA head to two terms in office. But there have also been press reports of U.S. phone intercepts of el-Baradei's office aimed at finding problems with his handling of a probe of Iran's nuclear program.
Washington's recent posture on UN issues seems to reflect an internal struggle. That's the view of James Dobbins, a former U.S. assistant secretary of state and international security expert at the Rand Corporation. "At the moment, there's a certain amount of internal tension, I would guess, within the administration about how far we should push some of these issues," Dobbins said. "My guess is the State Department certainly wasn't happy with the suggestion that Kofi Annan should be asked to resign."
Some U.S. resentment is directly linked to the Iraq invasion, which Annan has called illegal. El-Baradei said in advance of the war that he found no evidence Iraq had revived its nuclear program, a key U.S. claim.
Brian Urquhart served in top-level UN positions for nearly 40 years. He told RFE/RL the latest frayed relations also point to a core of UN skeptics in Washington who have found support in the current administration. "There is in some quarters in Washington an ideological objection to the whole idea of the UN," he said. "They just don't like internationalism. I mean, it's a perfectly reasonable point of view but it doesn't help the UN very much and I don't think that one should underestimate that."
One source of steady criticism of late has been Lakhdar Brahimi, a top aid to Annan. Brahimi played a key role in putting together the transitional government in Iraq. In his latest critique, Brahimi told an Arab forum earlier this week that the United States disregarded the human rights of Palestinians by failing to press Israel over rights abuses.
That drew a strong response from Tom Lantos, the ranking Democrat on the International Relations Committee of the House of Representatives. Lantos visited UN headquarters this week to express support for Annan but also complained about Brahimi's comments in his meeting with the secretary-general. "Brahimi is doing both the United Nations and the secretary-general personally great damage by his reckless and irresponsible public statements," Lantos said.
Annan later issued a statement saying Brahimi's remarks did not reflect official UN policy.
The up-and-down aspect to U.S.-UN relations can be traced to the origins of the world body, said Tom Weiss, who directs the Ralph Bunche Institute for International Studies at the City University of New York. Weiss told RFE/RL that he expects both parties to come together, especially due to the importance of the UN role in Iraq's transition. "We have these [low points] with some frequency and usually we bounce back because the organization plays an essential role in world politics," he said.
The United States is the UN's largest financial contributor, paying 22 percent of the regular budget and about 27 percent of its peacekeeping costs. It is also a major supporter of UN agencies providing humanitarian relief, electoral assistance, and other services.