Colt Industries, in an unprecedented action for a major U.S. weapons manufacturer, suspended sales to the public yesterday of its popular AR15 semiautomatic rifle, the civilian version of the military's standard M16. Mike Dunn, a spokesman for the company's Connecticut-based firearms division, said it acted voluntarily in response to the temporary ban on the import of foreign-made semiautomatic assault rifles announced by the Bush administration Tuesday. Dunn said the company would sell AR15s only to police departments and other government agencies while the federal government investigated how such weapons are being used. Gun control advocates, noting that the AR15 appears to be the most popular U.S.-made rifle among drug dealers, said they were pleased and stunned by the action. Kristen Rand, a Washington lawyer who has advised two major gun-control groups, said the voluntary suspension may have more impact on criminal use of firearms than Tuesday's import ban. "Colt's action definitely will have real effect, and I hope other manufacturers will see fit to follow suit." Although officials at the U.S. Bureau of Alcohol, Tobacco and Firearms said they had no estimate of the number of AR15s in use or produced annually, firearms experts said tens of thousands of the light, magazine-fed rifle are in private hands. Officials said that about two-thirds of an estimated 500,000 privately owned assault rifles in this country were domestically manufactured. Dunn declined to reveal Colt production figures but called sales of the weapon a "multimillion-dollar business." "Except for the {foreign-made} AK47, the AR15 is probably the most popular assault rifle among drug dealers," Rand said. Dealers say many legitimate gun enthusiasts are also willing to pay the higher cost of the AR15, about $700 compared with about $350 for an AK47, because of its close resemblance to the standard U.S. military combat rifle. Law enforcement groups have long put the weapon near the top of lists of rifles seized in criminal investigations. "I've seen an AR15 {bullet} go through four protective vests and still break a concrete block behind them," said Richard Inglehart, chief assistant district attorney in Alameda County, Calif. Federal drug czar William J. Bennett, who requested Tuesday's import ban, called the Colt announcement "an act of civic responsibility." Bennett called Colt president and board chairman David I. Margolis and was told by Margolis that the action came not in response to public "hysteria" but to the new government policy on assault rifles, a Bennett aide said. Tuesday's import ban did not affect domestic manufacturers such as Colt, and White House spokesman Marlin Fitzwater said yesterday that the Bush administration had "no plans" to expand the measure. Some industry experts acknowledged that U.S. suppliers might welcome even the temporary removal of cheap, foreign competitors from the market. "I suppose if you passed a new law banning Toyotas, General Motors might not complain about it," said Andy Molchan, president of the Florida-based National Association of Federally Licensed Firearms Dealers. Dunn said Colt decided to suspend its sales to the public anyway to honor "the spirit of the law." He noted that the company makes many other products, including aircraft landing gear and engine fuel injection equipment, and that the firearms division represented less than five percent of total sales. He declined to comment about how the decision might affect employment at Colt's single AR15 manufacturing plant in Hartford, Conn. The plant has been troubled by a long-standing labor dispute, with union employees on strike for the past three years. At the same time, Colt recently lost its longtime contract to provide the U.S. military with the M16 assault rifle. Colt has been criticized in the past for allegedly going out of its way to sell the AR15 to survivalist groups and other military enthusiasts who have sometimes come into conflict with the law. One 1985 advertisement cited by the Educational Fund to End Handgun Violence and New Right Watch showed "a handsome rancher" with "leather patches on the elbows of his flannel shirt and an AR15A2 in one hand." The advertisement said: "Survival means different things to different people . . . . For a rugged individual in the wilderness, it means being prepared for any eventuality." There were no immediate indications of other U.S. manufacturers suspending production of semiautomatic rifles. Some dealers said the import ban and Colt suspension might lead consumers to buy weapons like the Ruger Mini-14, but Steve Sanetti, general counsel for Sturm, Ruger & Co., Inc., of Southport, Conn., said that weapon was designed specifically for hunting and sports use and should not be considered a substitute for the AR15. The National Rifle Association, which called the import ban a chance to study how such weapons are used, declined to comment on the Colt announcement. Molchan said that gun control "does not mean crime control" and that criminals would always be able to obtain some lethal weapons.