Municipal Judge Harry H. Chandless Jr. is to preside this week in a hearing on what appears to be a simple zoning-law complaint, but he'll face difficult questions: At what point, if any, does a houseguest become a tenant, or a private home a boarding house?

Neighbors of a 53 Central Ave. family have complained that the address is being used as a rooming house, sheltering youngsters enrolled in a drug rehabilitation program.

"It's operating as a business," said Anita Guido of 47 Central Ave, whom the borough has subpoenaed to testify Wednesday. "Sometimes there are four, five, eight of them. Every other day another group comes."

The tenants at 53 Central Ave., Billy and Susan McCoy, say the complaints are ridiculous. "We're not running a boarding house," Sue McCoy said.

Though the borough filed the formal complaint, its officials are saying little about it.

An attorney for property owner Marie P. Sapio, also named in the complaint, said neighbors object to the McCoys' letting children from KIDS of Bergen Country Inc. stay over-night.

Billy McCoy declined to be interviewed, but a neighbor said McCoy recently went door to door asking neighbors to discuss the complaint.

Guido said that McCoy told her, "I'd like to explain about my kids," but that she declined to meet with the family. Apparently, so did everyone else McCoy asked. Borough Prosecutor Richard C. Gernert would not comment on the complaint. But a ranking borough official, who asked not to be identified, said the borough would argue that the housing of clients or patients enrolled in a program like KIDS is an inappropriate use in a single-family residential zone.

Victor A. Azar, Sapio's attorney, confirmed that "the McCoys do allow children from the program to spend the night."

"I understand one of the McCoy children is involved in this [KIDS] program," Azar said. He said that he didn't know whether the family is violating its lease, which began last Aug. 8; and that it is unclear whether the law is being broken.

The complaint, filed May 27, cited a 77-page ordinance adopted more than 50 years ago.

The lease says 53 Central Ave. is to be used "as a private residence" and for no unlawful purposes, Azar said. The complaint says it's being used as a boarding house, he noted, "but is that what's occurring here?"

He speculated that the borough's challenge might be legally construed as infringing on the right of free association.

Azar said there have been neighborhood rumors that activity at the house "created all kinds of disturbances."

A police official declined to comment, but Guido said there has been no cause to call the police. "They [KIDS clients] come in at 1 a.m. and they leave at 6 a.m.," she said.

KIDS, directed by Miller Newton, is not a defendant, and Newton refused to comment on the case. He said KIDS' tax-exempt status makes it a federal offense to divulge information about clients without their permission.

KIDS was a subject of controversy last year. Bergen County Prosecutor Larry McClure announced that a nine-month investigation had found no evidence to support allegations that KIDS staff members had physically abused clients, but he called for stricter regulation of privately run drug rehabilitation programs.

A state Department of Health spokeswoman said its Division of Alcohol, Narcotic, and Drug Abuse is reviewing the KIDS application for a certificate of approval. Whether the review will include the program's housing element, including placement of children in private homes, was not clear.

Newton, who has directed the KIDS program since its inception May 3, 1984, says it does not refer clients to boarding rooms or halfway houses.

What is provided, he said, is a "temporary environment" similar to a school exchange program in which families with youngsters in the program agree to accept other youngsters as overnight houseguests.

"It's strictly a voluntary thing," Newton Said. "No money is exchanged. It's similar toexchange student [programs]."

He said he could recall no other incident in which municipal officials or neighbors had complained' about a family's accepting clients from KIDS.

"This type of ordinance has been challenged in other states," said Thomas P. Monahan Jr., a Hackensack lawyer who represents KIDS. He said KIDS will monitor the case.