High-tech cops could soon be packing electromagnetic wave imagers that detect guns concealed under clothing and chemical tracers that sniff through walls to find hidden bullets.

Researchers say such technology has already been developed and would just have to be adapted for keeping streets safe and enforcing gun control.Law enforcement officials believe such sophisticated tools are badly needed.

"We have done little to modernize our primary crime-fighting instrument - the nation's police," said David Boyd, director of science and technology for the National Institute of Justice. "In fact, state and local police, who represent more than 95 percent of our nation's police personnel and handle well over 95 percent of the crime in this country, are still equipped such as was Wyatt Earp in the late 19th century."

However, civil libertarians warn that high-tech cops could trample on constitutional rights if care is not taken in weapons detection.

For instance, police couldn't legally use a portable electromagnetic detector to look for concealed guns on everybody walking along a city sidewalk, said Mike Godwin of the Electronic Frontiers Foundation, a group that studies legal implications of computers and other high technology. The Constitution strictly limits such warrantless searches, he said.

The House Judiciary subcommittee on crime and criminal justice held a hearing this year to examine how new technology can help in controlling illegal weapons and finding criminals. "America's highly sophisticated technology base can provide better alternatives and make our thin blue line more effective," Boyd told the subcommittee.

One useful new tool for police would be "passive millimeter wave imagers," said G. Richard Hugenin, president of the Advanced Technology Center of Millitech Corp. in South Deerfield, Mass., which makes the imagers.

He said these imagers can reveal both metallic and non-metallic weapons, plastic explosives, drugs and other contraband concealed under layers of clothing at a distance of 50 feet by using the millimeter wave portion of the electro-mag-netic spectrum.

Unlike X-ray detectors, "you're not irradiating people with these imagers," he explained. They rely on "existing natural emissions" of the various objects rather than on "man-made radiation."

Millitech's target price is $10,000. The first production prototypes will be available next year and, depending upon demand, larger-scale production could be under way the following year, he said.

"Using the hand-held version, a policeman on the beat could look from a safe distance and determine if a suspect is armed," he said. A fixed imager could show the actual weapon of anyone attempting to pass through a doorway with a concealed gun.

To find weapons and ammunition hidden inside buildings, high-tech cops could use a chemical analyzer to sniff out an "odorant vapor," said Russell N. Dietz, head of the Tracer Technology Center at the Brookhaven National Laboratory in Upton, N.Y.

Similar vapors are now added to natural gas so its presence can be easily detected. However, Congress would probably have to pass legislation requiring manufacturers to add such an odorant to guns and bullets.

A minute amount of such a chemical tracer added to the gunpowder inside a bullet, for instance, would diffuse through the casing and be detectable for 10 years, Dietz said. Using analyzers already in existence, police could find a single bullet hidden in a 10-story building, he said.

"From the outside of a building, you could sniff to see if you had any reason to go get a warrant" to search inside, Dietz said.

The manufacturer's cost of adding an odorant to weapons or ammunition would be negligible, Dietz said. And the tracing instrument, now about as large as a suitcase, could be reduced to "shoe box size," he predicted.

However, it would take a considerable effort to get such a system enacted, he conceded, so "the question is whether or not it makes sense to do it" given the other available technologies.

Meanwhile, the Supreme Court this week gave a boost to high-tech law enforcement. Without comment, the justices upheld the drug conviction of a St. Louis man whose marijuana crop was detected by federal agents flying over his home with a heat-seeking device.

The suspect claimed the Drug Enforcement Administration agents had violated his Fourth Amendment protection from unreasonable searches and seizures. The technology "allows the government to intrude into (the suspect's) home and gather information about what occurs there" violating his "reasonable expectation of privacy," his lawyers claimed.

The Court rejected this argument.

However, there are limits on high-tech searches, said Godwin of the Electronic Frontiers Foundation.

"That's why metal detectors at airports are set up near where planes are boarded rather than at front door of terminal," he said.