THE FAIRFAX COUNTY Board of Supervisors will be asked Monday to approve 77 new positions for the county's Department of Environmental Management (DEM) because current staff cannot keep up with the county's rampaging residential and office construction.

"We need the positions just to take care of the current building boom," said Denton Kent, chief of the county's Office of Comprehensive Planning. He said the requested staff additions will not cover pending applications for rezonings throughout the county.

DEM is responsible for applications, site plans, and ongoing and final inspections.

Currently, inspectors are spending about six minutes per inspection, Kent said, a figure that both builders and county officials agree does not give inspectors time to make thorough inspections.

The new positions, which the staff says are badly needed, will not all be filled by actual inspectors. Some are needed for support positions.

Several months ago, the Board of Supervisors okayed adding two building inspectors just to handle the work load generated by the beginning of construction of the giant 107-acre Tysons II mixed-use development in the Tysons Corner area.

IF YOU'RE PLANNING to sell or rent a house in Fairfax County, you better make sure the residence conforms with new smoke detector laws, which went into effect yesterday.

The new ordinance requires that all homes sold or rented must have a working smoke detector at the time of sale.

Old laws had required detectors in new homes but did not stipulate that the devices must be in working order. Now working smoke detectors must be in place in new or resale homes.

Local real estate agents are being told by their brokers that part of the responsibility for having the detectors working at the time of sale lies with the agent and the seller.

Tenants in rental properties will now be required to make sure their detectors are working and replace batteries. Tenants must notify property owners in writing when a smoke detector fails to function. Property owners are responsible for maintaining operating devices.

County officials are contemplating several ways of enforcing the new regulations but have not yet settled on a particular process.

A PROPOSED 1,764-UNIT subdivision on 365 acres in Gaithersburg, approved last year, is one step closer to construction as developers and Montgomery County worked out last week who will build the roads needed to service it.

The County Planning Board has already given the developers permission to build 450 units of the subdivision, called East Village, on the condition they make improvements to the intersection of Maryland Routes 15 and 124 near the proposed development.

Last week the board voted to allow 700 more units if and when the county decides to fund construction of two new roads that would be used by the residents of East Village, said Hugo Liem, county transportation coordinator.

The county has already included the two new roads in its capital improvements budget, which the County Council will vote on in May, said Liem.

He said the remaining units will be allowed when the developers lengthen the existing East Village Avenue to Route 124.

"Normally the county has been responsible for the building the infastructure, the roads, to support development," he said. "In the past few years, because of funding problems, developers have come forward and offered to build the infrastructure to get their developments off the ground.

"This is a case where the developers and the county are dividing the work," he said.

A $44 MILLION HOTEL-OFFICE complex is scheduled to open this summer along Sully Road near Washington Dulles International Airport.

The project, to be known as Renaissance Centre, is being developed by GT Renaissance Centre Limited Partnership, part of GT Realty and Management Co. Inc. of Alexandria.

The Renaissance Centre complex includes a 200-room Ramada Renaissance Hotel and a 300,000 square foot office building known as the Hallmark Building. The hotel and office building will be connected and are the centerpieces of a 170-acre business park which has been under development by the GT Group since 1968.

GT president Victor G. Trapasso said each person working in the business park can be expected to generate at least $1.50 per day for the hotel. "We can anticipate $5 to $8 million annually in business for the hotel from the offices which takes a lot of risk out of the development," he said.

PERSONNEL FILE . . . The Urban Land Institute has named James A. Cloar of Dallas as executive vice president. Cloar, currently president of Dallas CBD Enterprises, a public interest organization in Dallas, will take his new post April 1 . . . The Federal National Mortgage Association has named William A. Dawson to the newly created position of executive vice president-technology . . . Coldwell Banker Commercial Real Estate Services has appinted Michael Byard vice president/resident manager of its District office . . . The Montgomery County Housing Oppostunities Commission has reelected Mark Winston chairman and Robert Bell vice chairman. In addition, Marion Phillipps was elected chairman pro tem . . . Howard L. Flax has been promoted to manager of the Washington office of the Abacus Group . . .