Half of the houses in the United States now have smoke detectors, ten times the number five years ago, and the chances of dying in a residential fire have more than doubled for homeowners who don't have detectors, the U.S. Fire Administration reports.

But jurisdictions such as Montgomery County, Md., which have mandated that all homes have smoke detectors, reported to the International Association of Fire Chiefs Foundation that while 94 percent of the detectors have been installed properly, the devices failed to sound in 32 percent of the fires that broke out in these home. This was said to be an indication that smoke had not reached the serviced area or of equipment failure, a conference of fire officials was told here this week.

Steve Dossett, chief fire inspector for the Texas new town of The Wood Lands 25 miles north of Houston, described his area's installation of a cable television-monitored fire protection system, which he said makes The Wood Lands "the safest city in America for fire." More than tow-thirds of the housing units there are plugged into the monitoring sytstem, he said, and every dwelling is required to have a minimum of one smoke detector and a heat detector. The status of the heat detectors is monitored by a cable television computer system, which reports alarms to fire dispatchers.

Smoke detectors are required in houses, apartments and hotel rooms in Montgomery and Prince George's counties in Maryland and the District of Columbia. Northern Virginia jurisdictions require them only in new construction, with no requirement for retrofitting existing structures. In an interview here, Charles Rule, fire chief for Alexandria, said that a "southern lobby" or downstate builders, property managers and politicians would probably continue to defeat efforts during this year's Virginia state assembly to enact strong smoke detector legislation.

"The only way we're getting smoke detectors installed in Alexandria is if we have a fire," he said. "It's an emotional issue."

One high-rise building in Northern Virginia described by its managers as progressive when it comes to fire safety is the 14-story Fairfax Towers built by Mozel Development Co. two years ago in Falls Church. It has sprinklers in the hallways, a fire detection alarm panel monitoring all smoke and heat detectors and a one-way communication system with speakers in all rooms and elevators. There have been only a few minor fires in the building since it opened and the sprinkler sytstem has extinguished them all, said Leonard J. Collidge, director of operations for the managing agents. But in general, few buildings in Northern Virginia have these safety features, he said.

Smoke detectors don't do much to prevent deaths in the home. However, "if you don't have a fire exit plan for the house, make sure that everybody knows how to get out," observed Chester Schirmer, a consulting engineer who is chairman of a committee of the National Fire Protection Association, which writes standards for equipment.

Make sure that all residents redezvous at a pre-arranged place when they escape a house fire, Schirmer said, "so you won't have to search for a 5-year-old child."

Schirmer, who advises property owners on fire safety design, believes that architects should be taught about planning for fire exits and other safety features, but says that no architectural schools emphasize such courses.