By the end of 2008, the government says, the makers of albuterol ''rescue'' inhalers - used by millions of people to reopen airways during asthma attacks - will have to stop using the ozone-destroying chlorofluorocarbon propellants that power the devices.

Three decades ago, scientists discovered that the CFCs were damaging the atmospheric ozone layer that shields the Earth from harmful ultraviolet radiation, and the United States began to phase in a ban on their use.

The transition to other propellants for asthma inhalers has already begun. But some manufacturers have dropped out of the market, and others have encountered manufacturing snags.

The rest are struggling to meet increased demand, and doctors and pharmacists say they are beginning to see supplies of inhalers tighten.

Manufacturers say consumers buy 59 million rescue inhalers a year.