The U.S. Fish and Wildlife Service in September offered to withdraw all permits that allow state and federal officials to kill mute swans or shake and oil eggs to prevent them from hatching.

The offer, aimed at resolving a suit by the Fund for Animals, needs the approval of U.S. District Judge Emmett Sullivan and will be considered by the judge at a hearing Oct. 6 in federal court in the District of Columbia.

Maryland and other states had gotten permits to kill swans and grease or addle eggs to prevent them from hatching because of damage to the environment caused by the swans, which are not native to the United States.

The Fund for Animals challenged the permit issued to Maryland, and Sullivan granted an injunction prohibiting the killing of any swans until he issued a ruling.

Nicholas Throckmorton, spokesman for the USF&WS, said the federal agency decided to withdraw the permits because Sullivan “discouraged us from pushing this further.”

“The judge suggested if we, the service, tried to push this forward legally, we would not win.”

Swans are protected by the federal Migratory Bird Treaty Act. State and federal officials had tried to persuade Sullivan that they should be allowed to kill birds to control the population and reduce the damage swans do to valuable underwater grass beds.

Asked if the Fish and Wildlife Service would try again to issue permits to kill swans, Throckmorton said, “Our migratory bird management office hasn’t decided what they are going to do yet.” He said the agency will have to review the environmental assessment it made to justify the need to kill some swans.

Michael Markarian, president of the Fund for Animals, said the decision to withdraw permits “is a colossal step for thousands of graceful and majestic mute swans.”

He said swans have been unfairly blamed for environmental damage that is primarily caused by factory farms and inefficient sewage treatment plants.

Jonathan McKnight, associate wildlife director for the Maryland Department of Natural Resources, said the state will not be deterred from its determination to do something to control the mute swan population, which he estimates numbers about 3,600 in the Maryland portion of the Chesapeake Bay.

“To allow it to grow would be an ecological disaster. We have a responsibility not to let that happen.”

But McKnight said he doesn’t know what the state can do. “We are certainly shut down for the rest of this year,” he said.

McKnight agreed with Markarian that swans are not the major cause of the loss of underwater grasses, which environmentalists say are a key to a healthy Chesapeake Bay.

But he said the current population eats about 10.5 million pounds of underwater grasses each year.

“An expanding population of these things eating exclusively Bay grasses ... is only going to spell accelerating difficulty for those of us trying to restore the grass beds,” McKnight said.

“It is clear that they are a major problem for the Bay,” he said.