 IN a surprise move which risks consolidating the growing perception of him as a back-down, back-off leader, President Barack Obama announced yesterday he was giving up his plans to impose stricter air quality regulations for fear it would add to the country's economic and employment woes.  Waving the white flag to the business lobby and to Republicans who had vowed to make the new ozone rule a litmus-test issue in 2012, Mr Obama instructed the administrator of the Environmental Protection agency, Lisa Jackson, to scuttle impending regulations designed to tighten standards set by the Bush White House in 2008 that had been labelled too lax by many environmental scientists.  It came as employment data released yesterday showed job creation in the United States during august had essentially hit the buffers, further darkening the economic horizon. The grim results, which left the unemployment rate at 9.1 per cent, were far short of what Wall Street had expected.  In a letter to the House Speaker, John Boehner, earlier this week, Mr Obama conceded imposing the standards would have cost the economy between $19bn and $90bn. Eric Cantor, the majority leader in the House of Representatives, said it would also cost the country millions of jobs over ten years.  It appears Mr Obama saw himself in an impossible vice squeeze. While he has championed the environment, he also knows that the right was preparing to attack him for failing to respond to the joblessness crisis by lifting regulatory burdens and easing uncertainties for businesses.  He may also be calculating that his retreat, which is sure  