WASHINGTON — President Obama’s administration has proposed banning the manufacture and sale of one of the most popular bullets used in AR-15 semiautomatic rifles, a move that has enraged gun-rights advocates and caused a run on the ammunition at gun shops across the country.

The Bureau of Alcohol, Tobacco, Firearms and Explosives said this month that it planned to restrict the armor-piercing 5.56-millimeter “M855 green tip” rifle bullet because of new handguns that use the ammunition and pose a greater threat to the police. Previously, the millions of inexpensive green-tip steel and lead bullets sold each year were only for rifles typically used by target shooters and hunters.

“With few exceptions, manufacturers will be unable to produce such armor-piercing ammunition, importers will be unable to import such ammunition, and manufacturers and importers will be prohibited from selling or distributing the ammunition,” the A.T.F. said in a highly technical 17-page submission on Feb. 13.

The proposal would allow people to use up the ammunition they have already bought. Gun shops and firearms organizations on Thursday said there had been a rush to snap up cases of the bullets since the National Rifle Association and other gun rights groups sent out urgent alerts to their members.