It all started with the loud parties. They would last for two or three days, the neighbors said. It was the kind of thing that had not happened before on Grenoble Court, a tiny quiet neighborhood on a hillside in the Wheaton Woods section of Montgomery County.

Then the residents noticed that cars began arriving at all hours at the house on top of the hill, which had been rented this month to a man in his 20s. The cars had license plates from as far away as New Hampshire, and Florida. And sometimes the neighbors noticed that the visitors to the house looked "all stoned" - as if they had been taking drugs, one neighbor said.

Suspicious that the home was the headquarters of a drug-dealing ring, the residents, led by a retired police officer from the neighborhood, told the police of their observations and gave descriptions of the men living in the house. Then they began keeping an eye on the home at 4511 Grenoble Ct. They took down the license plate numbers of the cars that drove in and out. They opened their homes to narcotics officers who wanted to stake out the place.

Largely because of the efforts of the community, 21-year-old Gary Donaldson, who was renting the house, has been arrested and charged with possession of narcotics, possession with intent to sell LSD, and maintaining a common nuisance.

Donaldson had been under surveillance by narcotics officers before, when he lived in the Twinbrook section of Rockville, police said. But police said they were unware of his new residence until they were contacted by a resident of Grenoble Court.

"They did one hell of a job," a police investigator said yesterday of the resident's efforts.

"We were just very disturbed by what was happening. This is a family neighborhood," said one of the residents.

"There was a girl who couldn't even walk from the (Donaldson) house to my house where (her) car was parked. She had to be picked up and bodily carried by one of the boys. It's pathetic to see something like that," the resident said.

There are only about 10 homes on Grenoble Court, a working class neighborhood of one-story rambler homes priced in the $60,000 range.It was built about 25 years ago and some of the original homeowners still live there.

Yesterday, the community drew praise from Police Chief Robert J. di-Grazia, who said, "We're grateful that people would be concerned enough about their community to cooperate with the police . . . There has to be a partnership between the police and community to have an impact on crime."

Donaldson actually was arrested twice in the last four days on drug charges.

Police had gone to Grenoble Court Friday to investigate a hit-and-run accident. When they saw Donaldson leaving the court in his car, they stopped him to ask questions about the accident. The investigating officer then noticed night stick on the car floor, and began to search the rest of Donaldson's car.

Police say the officer discovered small quantities of cocoaine, heroin, marijuana, phencylidine (PCP) and LSD inside the car.

Donaldson later was released on bond. But through the information the community was able to provide, police obtained a search warrant for Donaldson's home. And Monday night, Donaldson was rearrested and charged with possession of narcotics paraphernalia and maintaing a common nuisance. Last night Donaldson remained in the County Dentention Center, since his bond on the earlier offense was revoked after the new arrest.

According to Cpl. George Ludington of the department's crime prevention section, it is rare for residents to become involved in policing their own neighborhoods.

"I'm sure many residents know about things going on in their community, but they don't come to the police because they don't want to ge involved or they fear retaliation. Criminals use this to their advantage," Ludington said.

Ludington said the crime prevention section will hold neighborhood meetings in communities where the residents want to organize a citizen effort to help prevent burglary, vandalism and other common crimes. It is part of the department's Friends for a Safe Neighborhood program, Ludington said.