THE PRINCE GEORGE'S County Council unanimously passed an unusual law this past week, the first of its kind in Maryland. It had the strong backing of County Executive Parris Glendening and the fire department. Home builders were a bit less enthusiastic. The law requires installation of automatic fire sprinklers in all new commercial and residential construction in the county by 1991. That's fine for high-rise apartments and other large multifamily units, but the law goes too far by adding new town houses and new single-family houses to the list.

About 137 county residents have died in fires in the past decade, two-thirds of them in single-family houses. This makes devices for fire prevention as serious a matter as the alarms that protect houses against intruders. But those alarms are not mandatory. In the case of sprinklers for detached houses, a citizen's right to choose the form and level of his own peace of mind should prevail. If a homeowner wants this type of system installed, he can choose it, but it shouldn't be mandatory.

Fire Department spokesmen say that these "quick activation residential sprinklers" would go off at 160 degrees, considerably lower than the temperature it takes to boil an egg. Water would flow at 13 gallons per minute with no automatic shut-off feature. Water would continue to cascade until someone arrived to shut it off.

Many folks, unfortunately, have experienced the home burglar alarm that goes off when a squirrel bounces against a window (10 minutes. . . 130 gallons). There's also the case of smoke alarms that go off by accident.

Manufacturers say the sprinkler systems will add only $3,000 to the cost of a house. They add that they will lower other costs -- allowing thinner fire walls, for example, or lower insurance premiums. No figures are available on the potential for water damage if a system malfunctions.

This law will save lives, and that's worth the cost of placing sprinkler systems in high-rise apartments or the garden-apartment variety of large multifamily dwellings. Making sprinkler systems mandatory for every new single-family home, however, is excessive. It could provide more headache than safet