CONCORD, N.H. — State and federal officials have reached an agreement in New Hampshire to help bring back the endangered New England cottontail.

The small, brown rabbit depends on dense, tangled, low-growing shrubs in younger forests to survive. Once large trees take their place, the rabbit’s habitat is destroyed. The range of the species has declined by 86 percent during the last 50 years because of habitat loss.

Under the agreement announced this week, the state Fish and Game Department will work with private landowners in Cheshire, Hillsborough, Merrimack, Rockingham and Strafford counties to help restore the thickets during the next 50 years. The goal is to enroll 3,000 to 5,000 acres to be managed as cottontail habitat.

“This sort of agreement hasn’t been developed for any species within the 14 Northeast states,” Tony Tur, an endangered species biologist with the U.S. Fish and Wildlife Service, said today.

The rabbit was named a candidate for Endangered Species Act protection in 2006. It is listed as endangered by the state of Maine and New Hampshire; it is extinct in Vermont. There are small populations throughout the rest of New England and in New York.

Aging forests, the growth of non-native plants and the presence of white-tailed deer that eat the same vegetation as cottontails have contributed to the rabbit’s decline. In Cape Elizabeth, Maine, an effort to clear some invasive plants from a park accidentally removed an area where the rabbits lived. The state has asked the town to set aside land elsewhere in Cape Elizabeth to make up for that lost habitat.

The agreement in New Hampshire allows the Fish and Game Department to provide assurances to volunteering landowners that their conservation work “won’t jeopardize the future use or value of the land if the species is eventually federally listed,” said Steve Weber, chief of the department’s wildlife division.

Land management activities include cutting vegetation to promote shrub development, planting seeds, controlling invasive plants and transferring some rabbits to the newly created habitats.

“Once you manage the habitat, it’s going to take a few years to condition to respond,” Tur said. “There’s a bit of a lag time.”

Tur said the landowners would be eligible for some money for their work, in addition to technical assistance from the department.

He said while there hasn’t been evidence of more rabbits in their existing populations, there have been some recent discoveries of existing, workable habitat. One example is a group of islands in the Narragansett Bay area on the north side of Rhode Island. Tur said biologists are looking at whether the rabbits can be reintroduced to those areas.