Quite right, Dr. Watson, it's a laser

The Sherlock Holmes of the 1980s may turn out to be - the laser. A growing number of American law-enforcement agencies are using lasers to detect fingerprints and do other detective work.

''The laser is replacing the computer as the most awesome tool in forensic science,'' said John Quattrocki, head of the two-year-old laser lab at the Chicago Police Department.

Within the past six months the Harris County Sheriff's Department in Texas (encompassing the Houston area) has installed a laser. Sheriff's deputies in Dallas County will plug one in within the next few weeks. The Illinois state crime laboratory has two on order. And several dozen other agencies are seriously browsing for systems.

The allure of lasers is their ability to pick up fingerprints that conventional techniques, such as powders and chemicals, won't. In the laser process a highly focused light beam is shone on an area where a print might be found. If one is detected, it will ''glow'' like a luminescent picture. A camera then photographs it.

Lasers are often better than traditional techniques at spotting prints on leather, wood, and plastic. They don't alter the prints in any way. And they can spot them on even the most dusty and dated objects: The FBI (owner of three lasers) has found a print on a piece of mail more than 40 years old.

In more than one case, police say, the laser has proved to be the edge in an investigation. For instance, sheriff's deputies in Potter County, Texas, used theirs to sniff out prints on Styrofoam cups, checks, and bits of tape. Chicago police once helped crack a case by finding evidence on a hair dryer that had been submerged in water.

Crime laboratories are finding other uses for lasers. Some are using them to examine documents: Under the glare of a laser, subtle differences in ink stand out, helping experts pinpoint forgeries. Lasers also can be used to spot fibers on clothing and other surfaces. And in tests they have spotted stains and body fluids, which could prove vital in sexual abuse cases.

Other research work - such as that of Dr. Roland Menzel, physics professor at the Texas Tech University - focuses on the especially difficult task of lifting prints from clothing and skin.

Nevertheless, because of their $30,000 to $60,000 cost lasers largely remain the luxury of big law-enforcement agencies.

Many police agencies - and the town fathers who approve their budgets - are hard-pressed just keeping a full platoon of men on the beat and squad cars up to date. Moreover, the machines require relatively expensive technical knowhow to operate and maintain. They are also power-hungry and require plenty of water for cooling.

Fewer than a dozen US police agencies now have laboratories equipped with the devices, and no more than two dozen worldwide.