Unless the request is approved, the US government would begin running out of money in mid-May to reimburse Pakistan for military assistance and by July the US army and marines would also be short of funds, Gates said.
In a report on what it described as "global terror", the US state department said that attacks in Pakistan more than doubled between 2007 and 2008 and have quadrupled since 2006.
"Pakistan's ... tribal areas provided AQ [al-Qaeda] many of the benefits it once derived from its base across the border in Afghanistan," the report said on Thursday.
It also warned that Taliban and al-Qaeda affiliates had increased the "co-ordination, sophistication and frequency'' of suicide and other bombings in Pakistan and were challenging the government's authority.
And it said that efforts to combat the Taliban in Afghanistan in particular needed a global approach.
The White House has made Pakistan and neighbouring Afghanistan a central plank of its foreign policy, with Obama ordering 21,000 more US troops to Afghanistan and asking congress for aid to assist the Pakistani army.
|Taliban fighters have been carrying out an
increasing number of attacks in Pakistan [EPA]
Obama has also put pressure on Pakistan to produce results in its efforts to combat the Taliban and al-Qaeda, saying in a news conference on Wednesday that he was "gravely concerned" about the security situation in the country.
The US has become increasingly worried about the stability of nuclear-armed Pakistan, an ally seen as vital to stabilising Afghanistan, as the Taliban have advanced from their Swat valley stronghold to within 100km of Pakistan's capital, Islamabad.
Obama's comments came after Pakistani troops were reported to have regained control of the main town in Buner district from the Taliban in the country's North West Frontier Province.
In total, attacks in South Asia, including Afghanistan and Pakistan, accounted for 35 per cent of the 11,770 attacks that took place worldwide in 2008, the state department report said.
However, the total number of attacks fell from 14,506 in 2007 and the number of deaths also dropped to 15,765 from 22,508.
The report said the threat from al-Qaeda in Iraq had diminished following defections and a loss of funding and control in key areas and "improved capabilities" of Iraqi forces and Sunni tribes' so-called Awakening Councils.
Iran was also strongly criticised as the "most significant state sponsor of terrorism", with the report saying Iran continued to employ "terrorism to advance its key national security and foreign policy interests".