The call, at a donor's conference in Tokyo on Wednesday, comes as attacks by Iraqi fighters have prompted Washington to shift funding from reconstruction to security.
The two-day donors' conference will assess the status of $33 billion in aid pledged to Iraq - of which only $6.7 billion has so far been spent amid chronic instability.
The United States last month shifted $3.46 billion of its $18.4-billion aid package away from reconstruction to restore security and governance and create jobs.
US Deputy Secretary of State Richard Armitage urged other countries to "step into this void" and spend money on Iraq's infrastructure.
"I think the electrical and water areas are two areas that would find great favour nationally," Armitage told a news conference.
The United States said the switch in funding would create 35,000 new Iraqi police officers, 16,000 new border control officers, and 20 additional Iraqi national guard brigades.
"We believe shifting a majority of money into the security area will allow us to stand up the Iraqi forces much more rapidly and bring much more rapid betterment to the security situation in Iraq," Armitage said.
Some 55 countries and organisations are taking part in the conference, the fourth donors' meeting for Iraq since the fall of Saddam Hussein last year, and the first since the interim government took over from US-led forces in June.
"We believe shifting a majority of money into the security area will allow us to stand up the Iraqi forces much more rapidly and bring much more rapid betterment to the security situation in Iraq"
US Deputy Secretary of State
Interim Deputy Prime Minister Barham Salih asked the donors to waive the $120 billion in debt left over from Saddam's rule, and called on the United Nations to play a more active role in Iraq.
"We need more UN support and we need it now. Please don't let the Iraqi people down," Salih said.
"The development and stability of Iraq cannot be driven forward through the barrels of guns. Assistance and aid in the short term is the key to destroying the causes of terrorism," he said.
But Ross Mountain, the UN deputy special representative to Iraq, said both international and local staff in the country risked being attacked or taken hostage.
"We are trying to find ways of moving ahead. But the situation does inhibit our activities. There is no doubt about it," Mountain said.
The Tokyo meeting is intended to examine the $33 billion pledged at the first donors' conference in Madrid in October 2003, as disbursement has been hampered by insecurity in Iraq.
Machimura (R) says Japan will
give $40m toward Iraqi elections
The interim government has said it would propose to the donors a wish list of commitments to 324 projects costing a total $43.5 billion, including 53 related to infrastructure.
Host Japan announced it would devote $40 million of the $5 billion it has already pledged to support Iraq's legislative elections due in January.
Japanese Foreign Minister Nobutaka Machimura said the money was being offered in the hope "that the elections take place successfully and on schedule".
Armitage said: "Elections have to be held by the end of January.
"This is a course on which we have embarked and it's one we won't waver from. And of course, elections have to be nationwide."
However, US officials have acknowledged the January vote could spark more unrest because of the violence.
Salih insisted that Iraq had already met other political deadlines including the June transfer of power and could meet this one.
"We are determined to prove the doubters wrong again and hold elections next year as planned. Our political process is on track despite the odds," Salih told the conference.