The Bush administration on Thursday backed a measured expansion of the U.N. Security Council (search), saying it likely would support the addition of "two or so" permanent members including Japan.

A wider expansion could be "possibly injurious" to the Council's effectiveness, Undersecretary of State Nicholas Burns said.

With several nations clamoring for seats in what would be the first major revision of the Council in 40 years, Burns said the administration also might back adding two or three nonpermanent seats.

Currently, there are five permanent members of the Council -- the United States, Britain, France, China and Russia -- all of whom have the power to block any resolution with a veto. Additionally, there are now 10 nonpermanent seats, rotating for two-year terms on a staggered, regional basis.

Burns said none of the new members, permanent or otherwise, should be armed with veto powers in the view of the administration.

Secretary of State Condoleezza Rice (search) confirmed U.S. support for a permanent Council seat for Japan in a telephone call to Foreign Minister Yuriko Kawaguchi (search).

On a related front, the White House urged Congress to oppose legislation that would withhold up to 50 percent of U.S. dues if the United Nations failed to enact certain reforms.

"We have serious concerns and ... we hope very much that that bill would not be passed in its present form," Burns said of legislation sponsored by Rep. Henry Hye, R-Ill., chairman of the House International Relations Committee.

Despite administration opposition, however, President Bush was not threatening to veto the bill if it is passed.

"Now, the Congress is absolutely right to take a hard-nosed attitude toward the need for reform, and we support Chairman Hyde and other members of the House who believe that the time has come for fundamental reform," Burns said.

Reassuring Congress, Burns said Bush and Rice have reform of the United Nations "at the forefront of their agenda."

In New York, Secretary-General Kofi Annan (search) said he was encouraged that the United States had joined with other nations to support reform of the United Nations.

In a statement, Annan proposed the United States "engage with the other member states and come up with a reform package" hopefully in time for a heads of state meeting in September in New York.

At the White House, presidential spokesman Scott McClellan said the administration was issuing a document later Thursday that would ask legislators to reconsider the bill.

The largest financial contributor to the United Nations, the United States finances about 22 percent of the organization's annual $2 billion general budget.

Japan ranks second, behind only the United States, and is a leading contributor of military supplies for peacekeeping operations, Burns said.

India, Brazil and Germany also seek permament seats on the Council.

The Council was last revised in 1965 when the number of nonpermament members was increased from 6 to 10. In 1971, China's communist government took over the country's permanent seat from the Nationalists.