WASHINGTON (Reuters) - The Bush administration is assembling an ambitious spending plan for postwar Iraq, with preliminary estimates it may seek up to $65 billion in coming weeks to bolster military operations and reconstruction, people familiar with the matter said on Wednesday.

Senior White House officials told key members of Congress they would propose the emergency spending package "sooner rather than later," most likely before President Bush attends the annual session of the U.N. General Assembly in New York on Sept. 23, sources said.

The proposed emergency budget request would be a dramatic change of course for the administration, which had not planned to ask Congress for additional money until late this year.

"We need to do this now. They're working on the numbers as we speak," Sen. Lindsey Graham, a South Carolina Republican, said after meetings at the White House.

The White House declined to talk about numbers and insisted no decisions had been made.

"We are still assessing the needs and listening to (the top U.S. administrator in Iraq Paul) Bremer and the commanders in the field about what the exact needs are. We are still working to determine the precise costs and we will work closely with Congress once we know the precise costs," White House spokesman Scott McClellan said.

Sources said the administration was discussing a range of funding options, the most costly of which would provide $55 billion to the Pentagon for military operations in Iraq and elsewhere.

In addition, the White House is considering asking Congress for $10 billion to expedite reconstruction efforts, from repairing Iraq's electricity grid to building roads.

The U.S. Agency for International Development could receive up to $2.7 billion, sources said.

The reconstruction package would also include an estimated $1 billion for Afghanistan, which, like Iraq, has been wracked by postwar violence.

GROWING CONCERNS

Congressional aides said the proposed request reflected growing concerns -- both within the White House and Congress -- about mounting violence and the slow pace of reconstruction.

U.S. occupation authorities in Iraq are running low on money and lawmakers have appealed to the White House to make its spending plans known as quickly as possible.

Bush has promised to give occupation authorities the resources they need to stabilize the country, but critics say he has yet to deliver.

Earlier this year, Congress gave Bush $79 billion to pay for the conflicts in Iraq and Afghanistan, including $2.5 billion as seed money for Iraq's postwar restoration.

By asking Congress for extra money sooner than expected, Bush could demonstrate his commitment to improving security and reconstruction before he appeals to other nations at the United Nations to volunteer their own troops to a multinational force.

To that end, Secretary of State Colin Powell said on Wednesday he began negotiations with key Security Council members on a draft U.N. resolution that would adjust the arrangements for running postwar Iraq.

A massive spending request could be politically risky for Bush.

The administration has played down the cost of reconstruction for months, although officials now concede Iraqi oil revenues will not come close to covering the bill as they had hoped.

A $65 billion request would also push the nation's budget deficit to well above the half-trillion-dollar mark for the first time.