The Economist, the respected weekly current affairs magazine, on Thursday said it was backing US President Barack Obama for re-election, although with less enthusiasm than four years ago.

The London-based publication said in its leader that while the United States faced a tougher decision and a more negative campaign than in 2008, Obama's Republican rival Mitt Romney "does not fit the bill".

"This choice turns on two questions: how good a president has Mr Obama been, especially on the main issues of the economy and foreign policy? And can America really trust the ever-changing Mitt Romney to do a better job?" it said.

"On that basis, the Democrat narrowly deserves to be re-elected."

The Economist said it had backed Obama "with enthusiasm" in 2008, as did millions of voters, but that Americans will in 2012 "trudge to the polls far less hopefully".

"So (in spirit at least) will this London-based newspaper. Having endured a miserably negative campaign, the world's most powerful country now has a much more difficult decision to make than it faced four years ago," it said.

The magazine, publishing its leader on its website ahead of the print edition on Friday, lambasted the "woeful nature" of Obama's campaign, saying that where he once "personified hope and centrism" he had resorted to low blows at Romney.

But while it said that Obama's achievements had been modest, Romney had flip-flopped on too many issues to be credible, while his plans to cut taxes and increase defence spending were unaffordable.

"For all his businesslike intentions, Mr Romney has an economic plan that works only if you don't believe most of what he says. That is not a convincing pitch for a chief executive," The Economist said.

"And for all his shortcomings, Mr Obama has dragged America's economy back from the brink of disaster, and has made a decent fist of foreign policy. So this newspaper would stick with the devil it knows, and re-elect him."

The Economist has a worldwide circulation of 1.57 million, with nearly 850,000 copies shifted in the United States alone, according to its publishers. Its website had more than 14 million unique visitors in July 2012.

In 2004 the staunchly economically liberal weekly backed Democratic challenger John Kerry against president George W. Bush.