Trouble on Wall Street could lead to vacancies on Cleveland's main streets, gutting floors of downtown office buildings as banks and financial-services companies merge, cut back or crumble.

Public officials and local real estate professionals are nervously watching for shifts beneath the city skyline. As they pinpoint potential holes, they're discussing ways to market downtown, lure companies from the suburbs and fill gaps with new businesses and, possibly, government offices.

The most obvious trouble source is National City Corp., which owns or leases roughly 740,000 square feet downtown. As PNC Financial Services Group takes over, the Pittsburgh-based bank is sure to shed some of National City's 2,000 downtown employees and cut office space in Cleveland's central business district.

"We could end up with a much softer office market than people would like," said David Browning, managing director of the CB Richard Ellis brokerage in Cleveland.