WASHINGTON, MAY 15 The United States has warned four nations campaigning jointly for permanent seats on the UN Security Council that Washington will not support their cause unless they agree not to ask for the veto power that the five current permanent council members hold, senior diplomats and administration officials said.

The four nations—Brazil, India, Germany and Japan—are unhappy about that position. ‘‘The Security Council is not like an aircraft, with first-class, business and economy seats,’’ said Ryozo Kato, Japan’s Ambassador to the United States.

The four are plunging ahead with an ambitious worldwide lobbying campaign. Japan has summoned more than 100 ambassadors and chiefs of mission from its embassies around the world to a rally of sorts next week in Tokyo, where Foreign Minister Nobutaka Machimura will press them to lobby their host governments for support.

Wolfgang Ischinger, the German Ambassador to Washington, said, “I’m sure we are doing the same thing, making sure every one of us knows how we can move this forward.”

Ronaldo Sardenberg, the Brazilian Ambassador to the United Nations, said, “Our whole diplomatic establishment is mobilised for this.”

Speaking to reporters on his flight home from Moscow last week, Prime Minister Manmohan Singh said it was “very important for the United States, given its importance in world affairs, to be supportive of India’s aspirations.”

Brazil’s Sardenberg said his country would propose that the four nations be granted veto power that they could not use for 15 years. In 2020, he said, the United Nations could hold a conference to decide whether to lift the ban on the use of veto power.

The four need the support of 128 nations, two-thirds of the United Nations’ 191 members, to amend the UN charter. They plan to make their case in the capitals of virtually every nation before the issue is scheduled to come up for a vote during the September meeting of the General Assembly, which will attract more than 100 world leaders.

Besides the four countries pooling their efforts, three African nations—Egypt, Nigeria and South Africa—are conducting vigorous individual campaigns for some of the six new permanent seats proposed in March by Secretary-General Kofi Annan. The purpose of the change is to have the council reflect the current balance of global power better than is the case with the original five permanent members—Britain, China, France, Russia and the United States—and 10 members elected to two-year terms.

The proposal Annan offered the General Assembly would expand the 15-member council to 24 members, with the six new permanent members not having vetoes, and three new two-year spots for rotating members.

As part of the four nations’ campaign, presidents, prime ministers, foreign ministers and other senior officials are travelling the world, visiting nations and regions far outside their normal orbits—sometimes seeming to make bargains.

A Brazilian delegation, asking for support during a visit to Sudan in February, told Foreign Minister Mustafa Osman Ismail that Brazil opposed the imposition of UN sanctions on his country, where the United States says genocide is under way.

A senior Japanese envoy was in Ethiopia last month. Joschka Fisher, the German Foreign Minister, visited Central America in November and East Timor in February.

In Yemen in March, Gerhard Schroeder, the German Chancellor, offered support for Yemen’s application for membership in the World Trade Organisation. Ali Abdullah Saleh, the Yemen President, said he supported Germany’s campaign for a seat on the Security Council.

Shyam Saran, the Indian Foreign Secretary, plans to visit Washington next week, in part to lobby for support, ahead of Prime Minister Singh’s visit in July. A senior Indian diplomat just returned from South America.

One reason these leaders and diplomats may be campaigning on the other side of the world is that, in this effort, no nation can count on its neighbours. Argentina and Mexico oppose Brazil. Japan is facing serious opposition from North and South Korea, as well as from China, where tens of thousands of protesters took part in angry anti-Japan demonstrations last month.

Italy opposes Germany, while Pakistan is trying to block India. And those two countries in opposition, along with South Korea, are leading a counter-lobby pushing a proposal that would not award new permanent seats to anyone.

Still, the four nations have found distant friends. Guinea and Ukraine have offered support for Brazil. Vietnam and China appear to support Germany.

So far, by some estimates, the group has recruited the support of as many as 100 nations—though ambassadors and others say the number is soft.

The United States’ view on the group’s effort remains uncertain, leading some diplomats to worry that Washington may actually oppose expanding the Security Council because it would dilute American power.

Fuelling that view, Shirin Tahir-Kheli, a special advisor to Secretary of State Condoleezza Rice on UN reform, told the General Assembly last month that the United States “would like to move forward on the basis of broad consensus.” But predicating anything at the United Nations on such a consensus can be read as a formula for inaction.

The one clear statement to come from Washington is the warning about veto power. Administration officials said they were opposed to giving new members veto power, out of concern that it might paralyse the Security Council.

Ambassador Ischinger of Germany said he was told of the American demand and added, “My country would like to have equal status; that would be preferred. But if there is to be a different status, we would certainly look at it.”

On the broader question of US support, Rice has sent conflicting signals. On one hand, during a visit to Tokyo in March she said, “the United States unambiguously supports a permanent seat for Japan on the United Nations Security Council.” But when asked about seats for India and Brazil during visits there, she offered statements nearly identical to each other in their evasiveness.

“We will look at the issue of Security Council reform, but it should not get separated out from broad UN reform, because we want this institution to be as strong as possible, and you are not going to get as strong as possible an institution unless you restrengthen all parts of it,” she said in Brasilia last month.

The Bush administration’s ability to block the four nations is indirect. If 128 Assembly members vote to allow them to join the Security Council, council members must accept that decision. But then they must submit the revised charter to their governments for ratification. The Bush administration could simply withhold the treaty from the Senate, meaning it would not take effect.

Most of the diplomats say they think none of the five permanent Security Council members would be willing to defy the view of two-thirds of the world. Still, leaders of the four nations say they remain only cautiously optimistic of their ultimate success.

“There are many problems on the way,” Manmohan Singh said. “I think I would not minimise the difficulties.”