Randy Wagner leans into the foyer of the concrete-reinforced sound chamber and cocks his ear. The room's two huge steel doors are ajar, and inside, a Federal Signal model BP100 police siren is shrieking at more than 100 decibels.

"Hear that?" Wagner yells above the racket. "At the very end? That like, hoohoo'?" There is a faint hiccup at the low end of the siren's wail, a barely discernible catch in the ear-splitting din leaking out the doors.

But Wagner, 33, a government physicist at the National Institute of Standards and Technology in Gaithersburg -- a connoisseur of the clamor pounding against the walls of the sound chamber -- hears it clearly. He muses aloud: He'll look into it.

Wagner lately has become an astute critic of the music of mayhem: a man who, even when off duty, keeps an ear tuned for the distant sound of emergency. He hopes that by studying siren noise, he can draft guidelines that respond to those who fear today's emergency beacons are too loud and harm the hearing of public safety crews, and also to those who believe the sirens may not be loud enough and discernible enough to alert motorists.

His work comes at a time when emergency sirens no longer cut through the din of everyday life as they once did. They must compete with the rumble of traffic congestion, thundering car radios and the growing legions of motorists distracted by cell phones and comfortably enclosed in air-conditioned vehicles designed to rebuff outside noise.

Siren companies have tried to counter by adding to the traditional "yelp" and "wail" features of sirens, additions that include the bone-rattling "air horn," the European-style high-low noise and an array of other burps and warbles.

In Britain, scientists have developed what Wagner calls "pink noise" -- a non-siren sound resembling static -- that experts there believe helps motorists locate the source of the sound more quickly. One New York City fire crew even tried -- unsuccessfully -- sounding the "William Tell Overture" as it ran calls.

All the new sirens are intended to produce noise that better penetrates sealed vehicles and gets emergency crews where they're going. Some experts believe the difficulty motorists have hearing sirens is leading to more accidents.

According to the National Fire Protection Association, the number of accidents involving emergency vehicles rose about 25 percent from 11,325 in 1990 to 14,200 in 1996, the last year statistics were available.

Motorists' difficulty hearing oncoming sirens "is probably a factor, given the fact that the auto industry is out to make cars as soundproof as possible," said Carl Peterson, assistant director of the NFPA's public fire protection division.

At the same time, however, there have been growing concerns among emergency workers about hearing damage from long-term exposure to the elevated noise levels.

In Philadelphia, for example, a dozen retired city firefighters filed suit against siren companies alleging that they lost their hearing as a result of their exposure to excessive siren blasts. The issue is of such concern in Montgomery County that firefighters are required to wear ear protection while making emergency runs.

Studies by the National Institute for Occupational Safety and Health have shown that firefighter hearing loss, from sirens and other things, reaches as much as 1.5 decibels per year of fire service.

"If someone puts in a 30-year career, you're looking at 30 to 45 decibels of hearing loss," said Randy Tubbs, a Cincinnati-based NIOSH expert who conducted the studies. A loss of 90 decibels is considered severe.

There is some talk that future warning systems might dispense with sirens altogether in favor of car radio or radar receivers that would warn of approaching emergency vehicles. But for now, police and fire departments are stuck with the siren.

"It's going to stay for simple reasons," said Jiri Tichy, professor of acoustics at Pennsylvania State University. "It's a simple and efficient device to generate sound."

A century ago, the herald of emergency wagons was the clanging fire bell. Later, according to those who have researched their evolution, crude sirens, probably hand-cranked, were used when a vehicle was going to an emergency, and the bell was used on the way back.

Sirens were more effective in those days because many motor vehicles were open, said John Barry of the Occupational Safety and Health Administration, who has studied sirens with the Philadelphia fire department. But as the decades passed and cars became enclosed, their impact was gradually lessened.

"Some people think sirens are a thing of the past," said Richard Gibb, executive vice president of Federal Signal Corp., of Oakbrook, Ill., a leading siren manufacturer. "We don't.

"A siren sound in any given locale communicates to the motoring public effectively: They don't put them on bread trucks. It's an emergency vehicle."

In Britain, though, scientists are exploring something new.

Deborah Withington, a principal research fellow at Leeds University, said her idea for a non-siren warning system came after she was struck by how hard it was to determine the direction from which a siren was coming.

"It's not to do with being in the car," she said in a recent telephone interview. "It's not to do with having your radio on. It's the wrong kind of sound. Sirens don't tell you what direction they're coming from."

Withington said she traveled with rescue squads for her study and videotaped motorists' responses to sirens.

She said her research indicated that more than half the time, motorists seemed confused about the direction from which the siren was coming. Sometimes they were very confused. "I have seen people in panic leave their vehicle in the middle of the road and run," she said.

Withington began searching for something that might work better, and came up with what she called "the white noise siren." She said it makes a "sheesh" sound, much like the hiss of static, and because it covers a wider range of frequencies than the siren, its source is more easily detected.

But it lacked the authority of an old-fashioned siren. So Withington combined the two. The result is what she said is a highly effective warning sound that goes something like: "wow-wow-sheesh, wow-wow-sheesh."

Tests in Leeds, Leicester and London -- "If it worked in London, it would work anywhere," she said -- found a 25 percent increase in motorists heading out of its way.

But there was also a downside.

Despite the new device's apparent effectiveness, police and rescue crews missed the full-blown racket and "adrenaline rush" of the old days, Withington said.

They found the reduced noise "disconcerting." Although she believes her invention will catch on, Withington said of modern-day emergency crews: "They need to have a siren on."

At the federal standards institute in Gaithersburg, officials have enlisted Wagner to review the performance of siren systems and draw up guidelines for their selection and use. He is examining not only siren performance, but also how the equipment should be positioned on emergency vehicles to best shield crews from the deafening wails.

Last week, he was concluding a review of 12 siren noises contained on a CD and pumped at full volume through a series of siren loudspeakers that blared into a specially calibrated microphone set up in the sound chamber.

Wagner, for the most part, remained in the quiet control room outside the safe-like doors of the 1,000-ton chamber, whose walls are made of fiberglass wedges to reduce echoes and whose floor sits on 57 huge springs to reduce vibration. "You don't want to go in there," he noted, when the sirens are on. CAPTION: Physicist Randy Wagner stands in a Gaithersburg sound chamber with a siren he's testing. CAPTION: Physicist Randy Wagner, whose research centers on siren sounds, stands with a dummy whose realistic ear canal is used in hearing tests.