IF YOU thought smoke detectors were the last word in home fire security, think again. For fire officials across the country see the little device as merely an initial salvo in the technological battle against a menace that takes more than 6,000 lives each year.

Get ready for what is being touted as "the air bag of the fire protection industry." Get ready for the home in-door sprinkling system.

The the past several years, the U.S. Fire Administration and the National Fire Protection Association have been sponsoring research into the development of low-cost, highly sensitive sprinkler systems to guard the nation's homes against property damage and loss of life. And while those systems might not be beyond the prototype stage for another year or more, officials are talking about changes in local building codes and ordinances that would require indoor sprinklers in every new home.

Already the movement has taken a foothold -- where else? -- in California. San Clemente last summer became the first city in the country to demand that sprinklers be installed in every new house and apartment building. Others are lining up to get on the fire wagon.

The need for sprinklers in America's living rooms and closets is not apparent to everyone, especially not to many in the construction industry who see them as an unnecessary and expensive gadget -- or at least say as much. Indeed, available statistics show sprinklers only slightly more helpful than smoke detectors in saving lives.

Supporters of sprinkler development, for instance, refer to studies conducted at the Applied Physics Laboratory of Johns Hopkins University. Johns Hopkins regularly investigates fire fatalities in Maryland and the Distric of Columbia. The results are often used in federal fire safety programs.

Between 1976 and 1978, the laboratory investigated 117 fires, which caused 171 deaths and nearly $3 million in property damage. "The major results of the study," reads the report to the National Fire Prevention and Control Administration, "showed that 157 of the 171 fatalities could have been saved and 181 of the 189 injuries could have been prevented if the best of the three fire protection systems [sprinklers] had been installed."

Sprinkler systems promise a 92 percent reduction in deaths and an 88 percent decrease in property damage. Sprinkler opponents, however, dispute the idea's supporters by citing the study's findings on smoke detectors: 89 percent of lives saved and 72 percent of property damage reduced. "In other words," says Donald Carr, technical director of the National Association of Home Builders, "the fire-death reduction is practically identical with either system, yet the cost difference between a sprinkler system and a smoke detector is tremendous."

Smoke detectors are available for less than $30. The cost for a typical sprinkler system in a 2,000 square-foot home is around $1,000.

Harry Shaw, coordinator of the U.S. Fire Administration's sprinkler program, agrees with the numbers. "But he [Carr] forgot the footnote." The Johns Hopkins report did not attempt to evaluate the "human factors" that led to deaths in homes where detectors worked as they were supposed to.

"It is well known that humans can react unpredictably under stress circumstances, including fire," the report said. "Many of the people in the cases studied showed signs of being unaware of the magnitude of the fire problem." In one case, a man walked right past an exit in his burning apartment and died.Another man escaped his burning house with his wife, but died when he went back in to call the fire department.

Shaw and other sprinkler supporters argue that even if a sprinkler system failed to put out the fire, it would at least suppress it long enough to give people time to collect themselves and escape. But that is only half the argument.

In San Clemente, at least, it wasn't just the superior performance of sprinklers that swayed city fathers, says the city's fire marshall, Gary Carmichael. It was money. Especially the perceived lack thereof as a result of California's Proposition 13.

"Proposition 13 has given us the economic benefit of transferring the cost of fire protection to the homeowners," said Carmichael. "We just can't keep building fire departments. They're too expensive."

Shaw, too, says, "We are rapidly approaching the bottom of the barrel as far as providing new fire services is concerned. "There are many communities fire services can't protect. They're saying, 'You can't build there.' When you start to talk about 35 million new homes, and for every 5,000 of those a fire station, you're talking about one hell of an expense."

But the sprinkler system safety officials want is still wating to be developed and approved. Graham Clarke, manager of engineering for Grinnell Fire Protection Systems co., a major sprinkler manufacturer in Los Angeles, says production is still at least a year or more away. The standards necessary to ensure its performance are still to be written.

Sprinklers, the ones common to industry and commerce, simply aren't good enough for home use. Those need bo be 6 to 10 times more sensitive, said Clarke. They also need to be more powerful so they can be placed where they will be most effective, (in sidewalls rather than on ceilings), as well as esthetically pleasing (nearly invisible). Put those requirements together and you have what some in the industry describe as a technical nightmare.

Ed Reilly, president of the National Automatic Sprinkler and Control Association, told the conference last September that "the sprinkler manufacturer will be faced with design dilemmas to which there appear to be no known solutions . . ."

(San Clemente preferred not to wait for the advanced system. "If you ask me," said Carmichael, "it's better to have one that doesn't work as fast than known solutions . . . ."

(San Clemente preferred not to wait for the advanced system. "If you ask me," said Carmichael, "it's better to have one that doesn't work as fast than none at all.")

If the new residential sprinklers do make it past the design stage, homeowners who opt for them voluntarily (or are forced to do so by new building codes) could see a reduction in the cost of whole house insurance coverage.

Ralph Jackson, manager of loss prevention with Allstate Insurance who spearheads sprinkler studies for the insurance industry, says discounts could amount to 50 percent on fire coverage, or 20 percent on whole house premiums, if sprinklers prove themselves.

"The whole question of rate reduction is predicated on the expectation that sprinkler systems will reduce the likelihood of property damage," Jackson said. Whether they do or not is what insurance and adjustment authorities expect to find out from tests recently conducted in Los Angeles.

"I think they [discounts] would be seen as incentives," said Jackson. "Discounts are not something that insurance companies take lightly."

And incentives, say fire safety authorities, are something sprinklers need badly. The need for increased fire safety, they say, is something only vaguely perceived by the public. The expected cost of sprinkler systems doesn't make the job of promoting them any easier.