In a challenge to the authority of local jurisdictions to regulate group residential facilities. Maryland Attorney General Francis Burch ruled yesterday that a Prince George's County ordinance requiring certification of juvenile care homes is unconstitutional.

State regulations, he said, must take precedence over local controls.

The attorney general said that because the Maryland legislature has given the licensing power to the state it has in effect "preempted this licensing field" and conflicting local ordinances must yield to state law.

Although yesterday's ruling applies only to Prince George's County, state and local officials agreed that it could also hamper the ability of Montgomery County to regulate nursing homes.

"The situation is somewhat similar with respect to nursing homes," George Nilson, Maryland's deputy attorney general, said yesterday, when asked if Burch's opinion could apply to local regulations covering other residential facilities.

In a case now pending in the courts, the state is arguing that Montgomery County officials exceeded their authority last May when they ordered the Wildwood Health Care center in Bethesda to close two of its five wings after county inspectors found some residents living in unsanitary conditions.

The center was not closed because corrections were made before the May 31 deadline.

Burch's decision was issued after Rex Smith, the director of the Juvenile Services Administration in the Department of Health and Mental Hygiene, asked whether local regulations could supersede state rules.

Smith said yesterday that his request for guidance from the attorney general did not result from any one case, but because he was concerned that operators juvenile homes, half-way houses and other group residential facilities would become confused by conflicting local and state regulations.

John Barr, deputy county attorney in Prince George's, said he had not read the opinion and was not certain what action, if any, the county would take in response.

Burch also ruled yesterday that a Prince George's County zoning ordinance requiring a special zoning exception for those group facilities housing more than eight people also poses "a potential conflict with state licensing activities."

"Facilities licensed by the state participate in the state's immunity from local zoning insofar as local zoning restrictions contravene state policy . . ." the opinion added.

Smith, the Maryland Juvenile Services administrator, said he does not believe Prince George's has stricter licensing rules than the state for juvenile homes. He added that the county law is more vaguely written, but he said the differences between the two sets of regulations is "minor and I think relative insignificant."

Frances L. Abrams, director of Montgomery County's Environmental Protection, said he had not read Burch's opinion and could not comment on its possible effect on the county's regulating authority.