WASHINGTON (AP) _ The government decision to allow some motorists to get on-off switches for air bags has thrust the controversy over the safety devices into the laps of parents such as Nina Kaull and Deanna Popielarz.

``I have mixed feelings about it. I just don't know,'' said Mrs. Kaull, who ferries her own 6-year-old and a neighbor's children to school in Washington nearly every day.

But Mrs. Popielarz, who car pools to school with her four children and other families' kids in Saginaw, Mich., said, ``I'm considering it. I think it's great to have the option.''

Motorists at risk of injury from air bags _ including short adults and those who drive car pools and must have a child in the front seat _ will be allowed to fill out a federal form and have the on-off switch installed starting Jan. 19.

It's a response to the outcry over 87 deaths from air bags in low-speed crashes. Most were unbelted or improperly belted. Air bags, now mandatory in new cars, also are credited with saving 2,600 lives.

Even as they announced the liberalized rule for giving some motorists' control over the safety devices, federal officials hastened to emphasize they believe people would be safer off leaving their air bags on and keeping kids out of front seats.

``We have made a difficult decision. Now it is the public's turn to make theirs,'' Transportation Secretary Rodney Slater told a news conference.

White House spokesman Mike McCurry called it ``a common-sense solution.'' President Clinton promised last December to make it easier for motorists to get air bags deactivated.

Under the new rule, vehicle owners in these four categories can get the on-off switches:

_Those who must put children in the front seat because they are in a car pool or have large families and must use every seat.

_Those who cannot sit at least 10 inches from the air bag.

_Those with medical conditions in which the air bag poses a special risk.

_Those who must put rear-facing infant seats in the front seat.

``This is a practical solution that allows you to turn off the air bag for someone at risk and turn it back on to preserve the lifesaving benefits for everyone else,'' said Slater.

The National Highway Traffic Safety Administration will start accepting requests for the switches Dec. 18 and allow dealers and repair shops to start installing them Jan. 19.

People such as Mrs. Popielarz know the ball is in their court.

The estimated cost of an air bag switch _ $150 to $200 _ wouldn't stop her from getting one, she said. And she would like the front seat in her minivan to transport more kids when necessary.

``But the problem would be if you forgot to turn the air bag back on for an adult, or turn the switch off for a child,'' she said.

Nobody knows how many consumers will deactivate air bags _ although some auto officials have estimated it could be several million.

Automakers, insurers and safety advocacy groups all emphasized that the vast majority of people benefit from air bags. They spent much of the day advising consumers to buckle up children properly and put children age 12 and under in the back seat. Some 40 percent of children ride unbuckled.

``Only someone who is very close to, or on top of, an air bag as it first begins to inflate is at risk of serious inflation injury,'' said Brian O'Neill, president of the Insurance Institute for Highway Safety.

The government estimates that switches could save the lives of 177 children and 45 adults in the next four years.

But if only 1 percent of the drivers who are not at risk use switches, there would be 42 additional deaths, the traffic safety agency said.

Four major automakers already have retrofit cutoff switches in the works and will send them to dealers starting early next year _ General Motors Corp., Ford Motor Co., Toyota Motor Sales USA Inc. and Nissan North American Inc.

Chrysler Corp. said it will develop switches.

Motorists would be required to read a brochure about the safety devices and sign paperwork under penalty of perjury certifying that they fit into one of several higher-risk categories.

NHTSA then sends the owner an authorization letter, and the owner takes it to a mechanic.