A 30-year old Montgomery County woman was shot and critically wounded yesterday when she got out of her car on a busy county road to confront three strangers who had been taunting and harassing her from their own car.

There was no discernible reason for the harassment, according to Montgomery police. It was "one of those unexplainable things," press aide Nancy Moses said.

The shooting occurred as Sandra E. Barker began walking, a baseball bat in hand, toward the three persons who had pulled up behind her car on the shoulder of Layhill Road.

Barker, who came here a few months ago from Port Royal, S. C., and was living in the Wheaton area where the incident occurred, was driving north on Georgia Avenue with a woman friend around 3 p.m. when, according to police, a silver Cadillac pulled alongside her car.

Near the Capital Beltway, the occupants of the Cadillac began taunting and shouting at the two women.Police said they had no idea what, if anything, prompted the taunts. Neither Barker, a sorter for a direct mail service in the county, nor her friend, who was not identified, knew the occupants of the other car, police said.

As Barker continued north on Georgia Avenue, the Cadillac disappeared. A few miles later, however, near the intersection of Georgia Avenue and Randolph Road, the auto pulled alongside again, police said.

After Barker veered into Layhill Road, the occupants of the Cadillac "somehow threw a large amount of water into Barker's car," Moses said. According to one account, the Cadillac's occupants squirted water pistols at Barker's car.

Irritated, according to Moses, Barker pulled to the shoulder. The other car stopped behind her. Taking a baseball bat from her car, Barker got out and, "as if to ask 'What's going on? What's this all about?' " began walking toward the other vehicle, Moses said.

Two shots were fired. One struck Barker in the left hip. The shooting occurred at 3:13 p.m. near a number of stores and within a few blocks of the Wheaton District Police Station, and officers were on the scene radioing a lookout two minutes later, Moses said.

The victim was taken to Suburban Hospital, where she was reported in critical condition after emergency surgery last night.

Within five minutes after the shooting, police stopped a car at Arcola and Lamberton roads. Three persons were arrested and charged with assault with intent to murder, police said. They were identified as Cassandra Floyd, 21, Gregory MacDowell Johnson, 19, and a 15-year old youth. Police said all were from Detroit and were reportedly "just passing through" the Washington area.