LONDON -- The dramatic decline of the U.S. dollar is aiding the American economic recovery but setting off alarm bells overseas, with corporate executives, politicians and pundits calling it among the biggest threats to the rebounds underway in Europe and Japan.

Mounting concern abroad over the shrinking dollar underscores how exchange rates have emerged as a growing source of friction, with many countries jockeying for the weakest currency to boost exports and protect their markets from foreign competition.

The U.S. dollar has taken a steep tumble -- down 18 percent against the euro in the past 12 months, and more than 40 percent against the South African rand and Australian dollar -- as U.S. officials have effectively diluted its value, printing money and...