WASHINGTON — What could be one of the proudest moments in American conservation — the removal of bald eagles from the threatened and endangered species list — has been delayed again as the U.S. Fish and Wildlife Service struggles to define a single word: disturb.

If the regal bird is ever “delisted,” as officials have promised, an eagle-protection statute from 1940 will be left to guide new development along the Potomac River and other places where eagles now thrive. That law makes it illegal to “disturb” an eagle.

But what does that mean? Annoy? Frighten? Injure? Kill? The national symbol, having overcome trophy hunting and DDT, now waits on a balky bureaucracy and a seven-letter verb.

“It turned out to be quite a complicated issue,” said Paul Schmidt, Fish and Wildlife’s assistant director for migratory birds.

The issue could have serious effects on development along the eagle-rich Potomac. Development projects and efforts to protect eagles have been in conflict here before, as in the 1999 furor when an employee at the National Harbor project in Prince George’s County, Md., cut down a tree that apparently held a nest.

Now, environmentalists fear the government will settle on a narrow definition of “disturb” — like one that prohibits only killing birds, injuring them, or driving them from their nests. That, they say, would be difficult to enforce and would allow developers to encroach ever more closely on eagle havens such as Mason Neck National Wildlife Refuge in Fairfax County, Va.

“There’ll be a lot more building, a lot more development activity, a lot closer to bald eagle nests than there were here before,” said Michael Bean of the New Yorkbased group Environmental Defense.

The eagles nearly disappeared from the continental United States, thanks to hunting in the 19th century and the eggshell-weakening pesticide DDT in the 20th century. By 1963, only 417 breeding pairs were left.

But then came a ban on DDT and new protections for the eagle, named an endangered species in 1967. The bird was upgraded to “threatened” in 1995, and today there are more than 7,000 pairs in the lower 48 states.

To crown the eagle’s comeback, the president announced it would be formally removed from the list. President Clinton said that in 1999.

After years of delays, an official in the current administration renewed the pledge in December. “By Feb. 16, the bald eagle will be delisted,” he said.

But that day came and went. Instead, the Fish and Wildlife Service — now under court order to make a decision one way or the other — set a new deadline of June 29.

One of the holdups is a big fight over a little word.

“We need to figure out what ‘disturb’ means,” said John Kostyack, senior counsel for the National Wildlife Federation.

The word is found in the Bald and Golden Eagle Protection Act, which will become the primary law about eagles if the birds lose threatened-species protection. It lists all the things one cannot do to the national bird: pursue, shoot, shoot at, poison, wound, kill, capture, trap, collect, molest, disturb.

Since February 2006, the Fish and Wildlife Service has put out two federal-register notices, held two public-comment periods, and compiled more than 30 pages of official reports — all to define a word that the American Heritage Dictionary sums up in nine lines.

It’s promised to announce a definition next month.

And no, it’s not worried about defining the word that comes before “disturb” in the eagle law. Mr. Schmidt, the migratory-bird director, said it’s clear to most people what “molest” means.

The dictionary, of course, says it means “disturb.”