The 250 muffler shops, tire installers and other grease-stained businesses that make up the tumbledown quarter of Queens known as Willets Point have long known that they could be wiped out to make way for a gleaming new convention center, New York City’s first outside Manhattan.

In December, when Mayor Michael R. Bloomberg broke ground for sewer mains and storm drains for Willets Point to open the way for the neighborhood’s transformation, the city’s Web site trumpeted a convention center, citing it as helping to create “New York’s next great neighborhood.”

But a month ago, the businesses learned to their surprise and bewilderment that Gov. Andrew M. Cuomo was proposing another, far grander convention center — at more than three million square feet, it would be the nation’s largest — as part of a mammoth gambling hall that would rise at the Aqueduct racetrack, six miles to the south.

Does Queens, they wondered, need two convention centers?

Jake Bono of Bono Sawdust Supply, which for almost 80 years has sold sawdust to circuses and horse farms, said that if the Aqueduct convention center was built, “that point-blank means there’s not even a need for a convention center at Willets Point.”