Fairfax County will seek state approval to impose criminal fines and jail time on landlords who allow single-family homes to be jammed with tenants.

The Board of Supervisors agreed yesterday to ask the General Assembly for authority to fine landlords or homeowners $2,500 a day and send them to jail for up to a year for violating the county's limit of four unrelated people under one roof -- a stiffer penalty than called for under the existing zoning ordinance, which has resulted in fines of $100 a day at most, said Michael Congleton, the county's deputy zoning administrator for enforcement.

Several board members said they were frustrated by the county's slow progress in curbing crowding, mostly involving immigrant residents in single-family neighborhoods. The problem has prompted complaints from nearby homeowners and concerns about safety code violations.

"It's a serious issue in neighborhoods throughout the county," said Supervisor T. Dana Kauffman (D-Lee), who asked that criminal fines be added to the supervisors' package of requests to the legislature, which convenes next month. "Our county inspectors need real teeth to stop this." Kauffman's southeastern Fairfax district is home to many immigrants.

The move toward criminal fines comes as Fairfax and its neighbors struggle to crack down on crowding of immigrants, who are flocking to the region because of its hot job market.

The Manassas City Council approved a zoning amendment last week that redefines a family, restricting the occupants of a home to the head of household, spouse, siblings, children, grandparents and grandchildren. That is a narrower definition than was allowed by the city's previous housing code, which described a family as two or more people related by blood, marriage, adoption or guardianship. The family head is now defined as the person with moral or financial responsibility in the home.

Officials in Fairfax, which allows extended families of any number to live under the same roof, said they will study the new Manassas ordinance and a similar one passed last year by Herndon as they consider other tools to curtail crowded housing. Supervisors said they face complaints from neighbors about noise, cars parked in yards and the potential hazards posed by what essentially are boarding houses. Such living arrangements may be affordable but often violate health and building codes, officials said.

The burden of criminal fines would fall on landlords.

"It sounds a little severe," said Mary Beth Coya, spokeswoman for the Northern Virginia Association of Realtors, whose 13,000 members include many lease and property managers. "Landlords are just not aware of the ordinances" against crowding, she said. She predicted that enforcing a criminal statute would be just as difficult as enforcing the current civil one.

A task force of Fairfax health, building and zoning officials devoted to reducing crowding is considering several other enforcement strategies.

One would involve inspections of rental properties to enforce and prevent violations. Another would impose occupancy limits when homeowners are given permits for housing additions.

"Right now our enforcement system is complaint driven," Kauffman said. "But sometimes a violation has been created in a home even before the neighbors find out."

County inspectors have investigated 585 complaints about crowding this year, Congleton said yesterday. He could not determine how many violations were found but said many complaints turn out to be unfounded.

Also yesterday, the supervisors approved a new towing contract for the police department that will require towing companies to accept credit cards as payment for releasing illegally parked cars and to provide ATMs at impound lots. About 33,000 cars are towed each year in Fairfax by companies that contract with the police or the Virginia Department of Transportation, police officials said.