GRANTS PASS, Ore. — Federal biologists are designing an experiment to see if killing the aggressive barred owl that has invaded old growth forests of the Northwest would help the spotted owl, which is protected.

The U.S. Fish and Wildlife Service announced Wednesday it is doing a formal study to decide whether to do the experiment, and laying out the terms if they go ahead. The study will be available for public comment and is expected to be completed by fall 2010.

“This is to be done experimentally so we can nail down whether, in fact, removing barred owls could improve spotted owl demographics, and also to look into the feasibility of doing that,” said Fish and Wildlife biologist Robin Bown, who is overseeing the evaluation.

The spotted owl went from a seldom-seen denizen of old growth forests to the cover of Time magazine in the 1990s as environmentalists forced the federal government to cut back logging on Northwest national forests to protect its habitat.

Despite the cutbacks, spotted owls continue to decline, most steeply where there are high populations of more aggressive barred owls that are native to eastern North America.

Though killing one species to protect another is not uncommon — on the West Coast, for instance, ravens are poisoned to protect threatened snowy plovers — a small-scale experiment with killing barred owls in northern California in 2005 created an uproar.

So Fish and Wildlife held meetings with interest groups to consider the ethical and moral implications of a larger experiment, and secured their agreement to look into an experiment, Bown said.

“There is a range of opinions” among scientists and interest groups, said Bob Sallinger, conservation director of the Portland Audubon Society, who took part in the ethical discussion. “We are still struggling with where we come down.

The highest priority needs to be placed on avoiding extinction, Sallinger said. But unless habitat protections continue for old growth forests where the spotted owl lives, “killing barred owls is not going to accomplish anything.”

Scientists believe barred owls migrated from eastern Canada across the Great Plains in the early 1900s, using forests that popped up as people controlled wildfires and planted trees around farms. They arrived in Washington in 1973, and their numbers have taken off in the past decade.

Bigger, more aggressive and less picky about food and forests than spotted owls, barred owls drove spotted owls to marginal territories, sometimes mating with them and sometimes killing them.

Controlling barred owls was a central strategy of the Bush administration’s overhaul of the spotted owl recovery plan to make way for more logging. That plan was challenged in court by environmental groups and is being reconsidered by the Obama administration.

Fish and Wildlife is considering doing the experiment in existing spotted owl study areas near Cle Elum, Wash.; the Coast Range of Oregon; and the Klamath Mountains of southwestern Oregon, Bown said.

The work could involve trapping or killing barred owls in half the area and comparing the reaction of spotted owls there to those in the area still beset by barred owls, Bown said.

“If we are going to remove them, a shotgun will probably be the method of choice, because it is most reliable,” she said. “There will be very strict conditions to have close to a 100 percent kill rate. We don’t want to be wounding animals. We don’t want to be teaching them. And we don’t want to be removing nontarget species.”

Public comments on what should be considered in the study will be taken until Jan. 11.