TRAVERSE CITY, Mich. — Dozens of U.S. House members urged federal regulators Tuesday to retain legal protections for gray wolves across most of the lower 48 states, saying the resilient predator could continue expanding its range if humans don’t get in the way.

A letter signed by 52 representatives urged the U.S. Fish and Wildlife Service not to drop wolves from the endangered species list in areas where it hasn’t already been done. The wolf has been designated as recovered in the western Great Lakes and the Northern Rockies after rebounding from near-extinction in the past century.

The comeback is “a wildlife success story in the making,” the lawmakers said in a letter distributed by Reps. Peter DeFazio of Oregon and Ed Markey of Massachusetts, both Democrats. But it added that because of lingering human prejudice, “federal protection continues to be necessary to ensure that wolf recovery is allowed to proceed in additional parts of the country.”

The Fish and Wildlife Service is trying to return wolves to the Southwest, despite court battles and resistance from ranchers. It’s also reviewing the status of wolves and their potential habitat in the Pacific Northwest, where perhaps 100 of the animals are believed to roam, and in the Northeast, which has no established population although occasional sightings have been reported.

“The outcome of these reviews will identify which, if any, gray wolves should continue to receive protections under the Endangered Species Act outside of the boundaries of the recovered populations and the Southwest population,” agency spokesman Chris Tollefson said.

A recommendation is expected in the next few months, he said.

An agency report last year proposed dropping the wolf from the endangered list in most locations where none are known to exist. In their letter, the lawmakers said that could prevent wolves from migrating to places where they once lived and where enough habitat and prey remain to support them.

They noted that lone wolves have wandered into northern California, Utah, Colorado and several Northeastern states. If re-established there, they would help restore ecological balance and boost the economy by drawing tourists, DeFazio said in a phone interview.

“I think a heck of a lot of Americans would be thrilled to hear or see a wolf in the wild,” he said. “It’s part of our natural heritage.”

About 2 million wolves once lived in much of North America but were all but wiped out in the lower 48 states by the mid-1900s. The areas where they have recovered represent only 5 percent of their original range, said Noah Greenwald of the Center for Biological Diversity.