Inpatient costs will increase by about $130 a day next year at the four major hospitals in the Fairfax Hospital System, reflecting the organization's expansion plans and the cost of keeping up with medical technology, according to the system budget sent yesterday to the Fairfax County Board of Supervisors.

The budget calls for a rate increase Jan. 1 that, combined with an increase in August, raises the average daily inpatient bill next year 16.8 percent, from $778.19 to $908.98, at the four hospitals: Fairfax, Mount Vernon and Fair Oaks hospitals in Fairfax County, and Jefferson Hopspital in Alexandria.

The average cost for an outpatient visit will rise from $195.49 to $226.58, a 15.9 percent increase. Because rates have risen marginally in recent years, the system's inpatient rates have increased 4.4 percent annually in the last four years.

The Fairfax County Board of Supervisors is scheduled to review the budget at its meeting Monday. Though the board has no authority to change the budget, it is expected to approve a letter to the system's board of trustees calling the plan "reasonable and clear."

The county, which owns Mount Vernon and Fairfax hospitals, leases the structures to the system under a long-term agreement. In exchange for $1 annual rents, which are meant to allow the system to maintain low hospital bills, the organization must submit its budget to the supervisors for comment. Three supervisors also are allowed to sit on the system board.

"We subsidize their rent, so we want proportionately lower increases" in hospital costs, Board Chairman John F. Herrity said yesterday. He said he believes the increases are about average for area hospitals while the quality of medical care is "arguably higher."

The increased costs for patients are primarily a result of two factors, according to a report on the budget submitted to the supervisors. General rate increases account for an additional $100 a day over last year. An additional $30 a day results from more sophisticated treatment made possible by new technology and other medical innovations.

According to a spokeswoman for Blue Cross-Blue Shield, hospital rates in the metropolitan area last year rose 8.7 percent, with Virginia rates up 10.1 percent, Maryland rates up 6.6 percent and rates in the District up 8.7 percent.

Supervisor Nancy K. Falck (R-Dranesville), a member of the hospital board, said pressure to raise rates could be reduced if projects in the capital improvement program were "stretched out a little." "I've told the FHS board that in the future, only do the 'got to haves' -- as I call them -- and not the 'like to haves.' "

According to the system budget, operating costs at the four hospitals will rise from $238 million this year to $273 million next year, an increase of 14.7 percent. Included in the increase are wage increases of $9.3 million, money for 381 new jobs, and $12.8 million for new programs, inflation, nursing recruitment and data systems.

The total capital budget is $35.2 million.

Among the projects to be financed by the capital budget are a $1.4 million, 20-bed obstetrics unit at Fair Oaks Hospital, an $8.2 million critical care expansion at Fairfax Hospital, $2.3 million for renovations of the surgical area and other parts of Jefferson Hospital and $2.4 million for new cardiac services and a new phone system at Mount Vernon Hospital.