WASHINGTON (AFP) - The US government budget showed a surplus in January for the first time since September as the overall budget deficit trended lower, Treasury Department data released Tuesday showed.

The federal budget had a surplus of US$2.9 billion (S$3.6 billion), the biggest January surplus in five years, the Treasury said.

In January 2012, the budget gap stood at US$27.4 billion.

The surplus caught analysts by surprise; the average estimate was a US$2.0 billion deficit.

The unexpected January surplus followed a US$1.2 billion deficit in December, which had marked a sharp drop from the average US$146.1 billion shortfall in the two prior months.

In January, revenues jumped 16.1 per cent from a year ago to US$272.2 billion.

Spending also increased but at a much slower pace, of 2.9 per cent, to US$269.3 billion.

In the first four months of the 2013 fiscal year that began on Oct 1, the federal budget gap has shrunk 17 per cent compared with the same period in 2012, to US$290.4 billion.

For the current fiscal year, the Obama administration forecast the deficit will come in below US$1 trillion for the first time in five years, at US$991 billion, or 6.1 per cent of GDP.

The United States reduced its budget deficit to 7.0 per cent of gross domestic product, or economic output, in fiscal 2012, down from 8.7 per cent of GDP in the prior year, under a tightening effort aimed at paring high debt and promoting sustainable growth.

With GDP growth weak - a 0.1 per cent contraction in the 2012 fourth quarter - and the unemployment rate at 7.9 per cent, many Americans feel the country is still in recession despite its official exit in June 2009.

A majority of 53 per cent of voters said the economy was in a recession, according to a poll released Monday by Quinnipiac University.