The Dietze Construction Group, a building contractor in the Washington, D.C. area, filed May 18 for protection from its creditors in U.S. bankruptcy court in Virginia. The company had planned to sell itself to Suffolk Construction Co., a much bigger Boston-based contractor, but the announced deal apparently had never been completed.

Based in Ashburn, Va., Dietze listed numerous creditors and several million dollars in unpaid debt. The creditors included concrete, electrical and mechanical subcontractors or suppliers.

Dietze had 2009 revenue of about $150 million while Suffolk’s revenue for the year was about $1.7 billion. Suffolk’s revenue was boosted by the acquisition last year of William A. Berry & Son, its chief competitor in the health care market in the Boston area.

Suffolk had established a Washington, D.C. area office in 2009 to tap into the mid-Atlantic market but Suffolk was clearly hoping its planned Dietze acquisition, which it expected to close in January, would expand operations in the region.

Dietze had built numerous government, institutional and commercial projects. The company had also built interiors, some of them very specialized and equipment-intensive. Exactly how the company developed financial problems isn’t clear as Dietze officials could not be reached for comment.

“The economy has had a tremendous impact on our industry as a whole, and Dietze is no exception,” CEO Ralph Dietze told the Washington Business Journal. “These economic realities have forced us to file Chapter 11.”