A US government department has been forced to eat humble pie for apparently advising its 67,000 employees to buy Japanese or South Korean cars.

The climbdown by the US Department of Health and Human Services demonstrated the clout still wielded by Detroit's embattled carmakers in spite of their recent failure to block the passage of tighter fuel economy rules in the Senate.

The advice that staff seeking to cut back on fuel costs would be better off buying a Toyota, Honda or Nissan than a Chevrolet, Ford or Dodge came in a departmental newsletter devoted to "energy efficiency behind the wheel".

Apart from an explanation of the technicalities of hybrid petrol-electric cars, the newsletter included a list of the top 12 "green" cars compiled by the American Council for an Energy Efficient Economy.

All 12 are Japanese and South Korean models. They include the top-selling Toyota Prius hybrid, the small Toyota Yaris, Honda Fit and Hyundai Accent, and hybrid versions of the Honda Civic, Toyota Camry and Nissan Altima.

Detroit complained vehemently, not least because General Motors, Ford and Chrysler have been strenuously attempting to prove their green credentials in recent months.

Ford builds a hybrid version of its Escape sport utility vehicle while GM has promised to put its Chevy Volt electric car into production by 2010.

The health department newsletter displayed a "simplistic approach that showed a prejudice against American vehicles", said Jason Vines, Chrysler spokesman.

On Thursday the department backed down, stating that it "deeply regretted that our newsletter offended anyone, especially those Americans working in the automobile industry and the millions of people who make American automobile manufacturers successful".