Xcel Energy is in the preliminary stages of seeking about 400,000 square feet of office space in a new building in downtown Denver.

If Xcel, Colorado's primary electric and gas utility, moves forward, it will represent one of the largest office leases ever signed downtown.

"It will be one of the biggest, most high-profile deals done in Denver for a long time," said Sam DePizzol, a tenant representative broker at CB Richard Ellis.

DePizzol said that Xcel is looking to consolidate into one new building downtown to create more operating efficiencies and save money, as well as moving into a "green," or super-energy efficient building.

"Being green is very important to them," DePizzol said. "All of these new buildings planned downtown will be LEED (Leadership in Energy and Environmental Design)-certified."

In downtown, Xcel has most of its work force in three buildings: 17th Street Plaza, at 1225 17th St.; 550 15th St., which is its former headquarters; and Granite Tower, 1099 18th St.

DePizzol and other brokers said that Xcel has hired Barry Dorfman of the Staubach Co. to study Xcel's options. Dorfman declined comment.

Mark Stutz, spokesman for Xcel, confirmed they have retained a commercial real estate broker, but gave no specifics of its plans.

"From our perspective, it is prudent to look at our real estate options and opportunities from time to time," Stutz said. "Anything we do has to be cost effective and beneficial."

DePizzol said Xcel has about "seven or eight choices," from various buildings under construction or on the drawing board downtown.

They range from the Two Tabor Center, which is proposed as a 40-story tower at 1200 17th St., to a $175 million, 14-story, 450,000-square-foot building proposed to be built at 16th and Wewatta Street.

When Colorado Springs-based Sunshine Development announced the project last week, it said it was negotiating with one unnamed tenant.

"It has to be Xcel," said Joe Cantalamessa, a broker with CB Richard Ellis. "It's the only deal out there of that size."