WASHINGTON (REUTERS) - A new US intelligence estimate predicts that gains the United States and allies have made in the Afghanistan war in the past three years will be significantly rolled back by 2017, even if some US troops remain, the Washington Post reported, citing officials familiar with the report.

The National Intelligence Estimate also predicts that Afghanistan will quickly fall into chaos if Washington and Kabul fail to sign a security pact to keep an international military contingent there beyond 2014, the newspaper said on Saturday. The pact must be signed for the United States and its allies to provide billions more dollars in aid to the impoverished country.

The newspaper cited officials who have read the classified report, which includes input from the 16 US intelligence agencies, or were briefed on its conclusions.

"In the absence of a continuing presence and continuing financial support," the intelligence assessment "suggests the situation would deteriorate very rapidly," the newspaper quoted one US official familiar with the report as saying.

But the newspaper said some officials felt the report on the potential outcome of the longest war in US history was overly pessimistic and did not take into account progress made by Afghanistan's security forces.

"I think what we're going to see is a recalibration of political power, territory and that kind of thing," the paper quoted one official as saying.

"It's not going to be an inevitable rise of the Taleban."

Afghan President Hamid Karzai has balked at signing the security pact that would permit US forces to stay in the country beyond 2014, and US officials have said that unless a deal is reached to keep perhaps 8,000 US troops, the Taleban insurgents might stage a major comeback and Al-Qaeda could regain safe havens.