The United States has reiterated its opposition to a legislative proposal that would withhold U.S. dues to the United Nations.

The Bush administration says it is opposed to legislation passed by the House of Representatives that would withhold U.S. dues to the United Nations by up to 50 percent if the world body does not implement reforms.

At a Senate Foreign Relations Committee hearing, Undersecretary of State for Political Affairs Nicholas Burns said there is momentum at the United Nations for reform, and he urged the Senate not to back the House measure. "If we withhold funds, and we are very much opposed to that, then we are convinced the United Nations will be less successful," he said.

In the wake of a number of scandals at the United Nations, including allegations of corruption in the Iraq oil-for-food program and reports of sexual abuse by peacekeeping troops, the world body is to hold a summit on reform in September.

Ambassador Burns expressed confidence that a number of reforms would be adopted at the meeting, which President Bush plans to attend.

Among the proposals under consideration include expanding the 15-nation Security Council, changes in management, and reforming the U.N. Human Rights Commission.

Ambassador Burns said a law requiring a withholding of U.S. dues would impede on the president's constitutional authority to conduct foreign affairs.

Senate Foreign Relations Committee chairman Richard Lugar, an Indiana Republican, agreed.

The Senator, along with Senator Norm Coleman, a Minnesota Republican, has introduced legislation that would give the United States the option, not the requirement, to withhold dues if the United Nations does not act on reforms.

"Without narrowing the president's options, the Coleman-Lugar legislation allows the president to make tactical judgments in the national security interest about how to apply leverage and about what methods to use in pursuing reform," he said.

Ambassador Burns said the administration favors the Lugar measure over the House-passed legislation.

Former House speaker Newt Gingrich, the Republican co-chairman of a congressional task force on U.N. reform, said the president should have the authority to withhold dues.

But his Democratic co-chairman, former Senator George Mitchell, opposed the idea of withholding dues. "If we say, "Here is our list of reforms. If you do not adopt them, we will withhold." What is to stop Japan, Germany, the United Kingdom from presenting their list of reforms, and if they are not adopted, they will withhold. It seems to me there is a very dangerous potential there all the way around," he said.

The top Democrat on the Senate Foreign Relations Committee, Senator Joe Biden of Delaware, agrees, saying any such legislation on withholding dues would undermine U.S. credibility at the United Nations.

He recalled the 1990's, when the United States withheld U.N. dues and nearly lost its vote in the General Assembly after it accrued high arrears.

The United States is the largest donor to the United Nations, contributing 22 percent of its operating budget.