Side air bags will soon be much more common in cars on the American road.

Ford Motor Co., concerned by the death rate of people in cars hit from the side, announced Wednesday that it will offer side air bags on all of its cars and Ford Windstar minivans over the next two years, Ford officials said.Ford is the first mass-market automaker to offer side air bags on all its cars; it has not previously offered such devices on any of its U.S. models.

General Motors Corp. already offers side air bags on a half-dozen of its 81 models. And GM said Tuesday that it plans to add 15 more over the next two years. Luxury car makers like BMW, Mercedes-Benz and Volvo also offer side air bags, and now Ford and GM think their customers will want them, too.

Ford's side air bags will be built into the outer side of both the driver's seat and the front passenger's seat and will inflate to protect the occupant's neck and head. They will be offered first as options on the new Mercury Cougar coupe this spring and the redesigned Ford Windstar this autumn.

Ford said that by the 2001 model year, side air bags would be optional or standard equipment on all its cars. The side air bags will be standard equipment on Ford's luxury cars, particularly Lincoln sedans.

They will become standard equipment on less-expensive models as soon as buyers start consistently choosing them as an option, said a Ford executive.

Side-impact collisions have in recent years accounted for a growing proportion of all deaths in traffic collisions - now a quarter of all such deaths - as air bags and seat belts have made frontal collisions less dangerous.

Federal regulators, insurance industry researchers and the automakers' own safety experts have been increasingly worried in recent months that the spread of light trucks, including sport utility vehicles and pickup trucks, may make more of these collisions deadly.