SAVANNAH — The Navy can build a $100 million offshore range for submarine warfare training, despite environmentalists’ fears that war games would threaten endangered right whales, a federal judge ruled.

U.S. District Judge Lisa Godbey Wood ruled the Navy took a “hard look” before concluding risks to the rare whales would be minimal at the proposed training site 50 miles off the coast of south Georgia and north Florida. Environmentalists sued to block the project in 2010, saying it’s too close to the waters where right whales give birth to their calves each winter.

The groups that sued said Monday they’re weighing an appeal. Experts say only about 400 right whales remain, and each death brings the species a significant step closer to extinction.

“They are critically endangered and I think deserve a weight beyond other species,” said Sharon Young, marine issues director for the Humane Society of the United States, one of the groups that sued the Navy. “We certainly would never argue to undermine our national defense, but it’s also reasonable to ask the military not to jeopardize a species that is just barely hanging on.”

The proposed training range would consist of 300 sensors connected by a web of cables on the ocean floor in an area covering about 500 square miles. The Navy, which has bases nearby in both states, would use the site to train with a mix of submarines, surface ships and aircraft.

The Navy plans to begin construction as soon as 2014 and begin training on the site in 2018, said Jene Nissen, the range’s program director and a retired Navy commander. He said further environmental studies the Navy conducted since the lawsuit was filed only reinforced its conclusion that right whales won’t be at risk.