It was a suspicious vehicle for several reasons, the Montgomery police recalled. The three occupants were "lowriders," their heads barely visible from the street. Then two of them stepped out and disappeared from view while the driver, looking nervous, backed into an alley to be ready for a quick exit.

Thirty minutes later, the men ran back to the car, oblivious to a dilapidated sedan parked nearby and the police officer inside it who radioed four other unmarked patrol cars stationed in the area. When a robbery was reported minutes later over the police radio, the police team already was on the tail of three suspects. After a chase through Silver Spring, the suspects were captured.

To Montgomery County police officials, the incident last spring was a good example of how their five Special Assignment Teams (SAT), 35 plainclothes officers who patrol the county in unmarked cars and vans, are supposed to work. Established in February in response to a sharp increase in crime in the county, the teams made 405 arrests in their first five months, according to police statistics, mainly because they were at the scene and witnessed crimes when they occurred.

"You've got to be aggressive in this business," says Sgt. Raymond E. Griffin Jr., clad in a typical "uniform" -- a tattered, blue mesh "One Flight Up" T-shirt, old jogging shoes without socks and a pair of jeans that have seen better days. "By the time a crime is relayed to an officer on his radio it's ancient history."

The arrests also are more likely to hold up in court. "We haven't lost any robbery cases in court since September 1980," says Griffin. "The convictions are easier since the prosecutors don't have to rely on untrained witnesses."

Employing sports terms like "zone," "prevent," and "man-to-man," as well as hand-held telescopes, binoculars, policewoman decoys and disguises, the team has three main tactics: "saturating" a crime ridden area, following anyone displaying suspicious characteristics, or tailing known suspects.

"Within five minutes you can tell if someone has legitimate business here," says Griffin. "You watch for people constantly looking around and over their shoulder, nervous activity, lowriders, groups of people who leave one person in the car at the wheel."

Montgomery SAT teams once existed on a less elaborate basis, but were reduced or eliminated when officials said more officers were needed on regular patrol, according to police spokeswoman Nancy Moses. A drastic increase in crime over the last three years convinced Police Chief Bernard Crooke and County Executive Charles Gilchrist to reinstate the teams last spring.

Alexandria had a similar unit, but disbanded it last year because of a shortage of manpower. Prince George's and Fairfax counties have centralized Special Operations Division based out of police headquarters and the Washington police handle somewhat similar duties on a district by district basis, depending on crime patterns, say spokesmen. Only Montgomery places regular units on patrol in each of their districts.

In Silver Spring, for example, the SAT team concentrates on the business district near the District of Columbia line, where the idea is to infiltrate the streets, perhaps wiring a female officer for sound in high crime areas and maintaining surveillance on them. "We'll create our own victims if they can't find one," says Griffin. The officers also will tail women on their way home, watchful for any potential assailants.

"We deal mainly with larcenies and strong-arm robberies in the commercial sections. There are a lot of shoppers, a lot of money on the street," Griffin says, adding that the teams will call in a "10-70" over the police radio when they feel they have a possible crime set-up. That call warns marked police cars to stay away from the surveillance area. "We'll use everything from vans to Volkswagens when we work."

The teams also use elaborate surveillance techniques such as parallel tailing (deploying cars on parallel streets while another car follows a suspect from behind) according to Griffin.

In one of the most involved surveillances, lasting for 16 hours over a three-day period, the SAT's female officer was wired for sound while unmarked units were stationed nearby, Griffin said. A carload of male assailants eventually were arrested when they tried to attack her in a telephone booth, Griffin said.

"At one point, they pulled up and parked right next to one of our cars while our officers were pretending to be asleep," Griffin said. "They sat there discussing the whole robbery plan while we listened."