Unemployment ebbs and flows, but one measure of the nation's economic health, average weekly wages, rarely dips.

Until now. In the latest demonstration of the struggling economy that threatens President Obama's reelection, average weekly wages fell in 2011, one of only five declines since the category was created in 1978 by the Bureau of Labor Statistics.

In a just-released review of employment in the nation's largest 322 counties, BLS found that weekly wages dropped over the year by 1.7 percent to $955 in the fourth quarter of 2011 from a high of $971 in the fourth quarter of 2010.

That means the $50,000-a-year mark, busted in the fourth quarter of 2010, has dropped back to an average yearly salary of $49,660. And the wage depression was widespread: 282 major counties suffered wage declines; just 36 saw increases.

The wage drop comes as employment has increased in a majority of the counties in the last quarter of 2011, said the agency. That irony makes it the only quarter in history where wages shrunk while employment grew, a grim reminder that more Americans are taking additional jobs to make ends meet.

The Labor Department agency added that smaller bonus payments in the fourth quarter helped to push weekly wages down.

Two Virginia counties figured in the drop in wages. Of all large counties reviewed by BLS, Arlington County registered the fifth largest weekly wage cut, $84, and Loudoun County came in ninth with a $60 a week cut.

Still, Virginia and Washington are where the big paychecks were cut. New York City had the highest average weekly wage in the fourth quarter of 2011 at $1,899. Washington was third at $1,668, Arlington County was sixth with $1,591, Fairfax County ninth at $1,512 and Alexandria City tenth with an average weekly wage among workers of $1,434, said BLS.

The president has been making the case that job growth has occurred on his watch, but the wage stagnation opens the door for GOP foe Mitt Romney to hit Obama's handling of the economy, said associates.