Howard Decker, the knowledgeable, affable chief curator at the National Building Museum for the past four years, abruptly resigned this week. His last day at the museum was yesterday.

Chase W. Rynd, the museum's executive director, announced Decker's resignation in an e-mail Thursday afternoon.

Rynd, who has led the museum since July 2003, cited no specific reason for the departure. He did say, however, that "as a result" of the resignation he is abolishing the position of chief curator "in favor of a format in which our various curators report directly to me."

In an interview, Rynd explained that he wants to replace Decker with a curator who is not "overly burdened with administrative tasks" and who takes direct charge of certain exhibitions.

"I'm happy to get out of his [Rynd's] way and give him the room to do what he has to do," Decker said yesterday. "I always thought of coming to Washington as an exploration, and now I'll see how the exploration continues." He said he was looking at various possibilities around the nation in the architecture field.

Both Rynd and Decker say the parting was amicable.

Decker came to the Building Museum from Chicago, where he was a founding principal of DLK Architecture, a firm that designed award-winning buildings and also took part in large-scale urban infrastructure and transportation projects.

At the Building Museum, Decker oversaw numerous popular exhibitions, including "Big & Green: Toward Sustainable Architecture in the 21st Century," "Masonry Variations" and the current "Liquid Stone: New Architecture in Concrete."

Rynd's previous experience is in art museums, and early in his career he was a financial analyst and portfolio manager in New York. From 1998 to 2003 he was executive director of the Frist Center for the Visual Arts in Nashville, and for five years before that he headed the Tacoma Art Museum in Tacoma, Wash.

Yesterday was Howard Decker's last day at the museum.