BRUNSWICK, Maine — Most of the work already completed at the Maine Army National Guard 133rd Engineering Battalion’s new headquarters is underground, so it doesn’t yet look like much.

But Guard officials say that, when it’s done, the ultramodern, $23 million structure will be a sparkling example of efficient design and environmental sustainability.

“Right now, the building is about 20 percent complete,” said Marc Dube, civilian assistant project manager from the state’s department of Defense and Emergency Management. “All of the work done so far is site grading, installation of underground utilities — piping, water, geothermal pipes, the slab foundation and retaining walls.”

Scheduled to be occupied in October 2014, nothing about the design of the new armed forces readiness center is typical, according to project manager Col. Normand Michaud — including its physical footprint.

“It’s a odd-shaped building, with all sorts of strange jogs (in the outline),” Michaud said, “but it’s pretty much a state-of-the-art building.”

Funding for the center comes from the U.S. Army. At 59,000 square feet, the headquarters will house 189 people from three separate units — the Headquarters Company, Forward Support Team and 1035th Survey and Design Team — within the Maine Army National Guard 133rd Engineering Battalion.

Everything about the building is intended either to conserve or reduce energy consumption, or find ways to recycle it.

JCN Construction, of Manchester, N.H., is the general contractor, chosen in part because it has completed other commercial or educational projects like this before, Michaud said.

It was designed to carry a “silver” rating according to Leadership in Energy and Environmental Design standards, a series of architectural requirements that buildings have to meet in order to be called “green.”

Low-flow fixtures and “rainwater harvesting” — through a 2,000-gallon rooftop tank collecting water for bathroom use — will help curb water use.

The sun also figures heavily into the building’s design. It will use solar hot water heating in summer, and natural gas for winter water and climate control. In addition, a glass “solar wall” will provide much of the natural light and heat for the interior, while photovoltaic panels rated at 38 kilowatts will supplement electrical needs.

All of the training center’s glass will have high “R” values, meaning that the windows are coated to keep heat from bleeding out in winter and retain cooled air in the summer.

Because so much natural ledge and rock exists around the site, a passive radon detection and removal system also is built into the slab foundation.