By Thomas Grillo
Banker & Tradesman Reporter

A downtown law firm wants out of its space at One Post Office Square, a property in Blackstone Group’s Boston portfolio, according to a source familiar with the negotiations.

Sullivan & Worcester LLP is seeking up to 130,000 square feet of office space in Boston. Today, the law firm is paying in the high $40s per square foot, the source said, though rent may double if Blackstone moves ahead with its rumored plans to hike rents across its portfolio.

The firm’s lease at One Post Office Square, a 40-story tower in the city’s Financial District, is expected to expire in 2011, the source said. “They’re evaluating their options,” said another source about the corporate law firm that provides counsel to clients ranging from emerging businesses to Fortune 500 companies.

Commercial real estate brokers say the combination of a sluggish economy, Wall Street’s gyrations and the credit crunch have stalled the region’s office market.  Tenants are staying put waiting to see if companies downsize and whether premier space becomes available at reduced rates.

“Tenants are convinced there will be blood and that there will be space available,” the source added.

Leah Schloss, Sulivan & Worcester’s marketing director, said no one at the company would comment on the potential deal.