The Metro board approved a fare package yesterday that will increase most base fares to 65 cents, raise boundary crossing fees and probably push more passengers into private cars. The higher fares, Metro's third such increase in 17 months, go into effect early next month.

The new fares are projected to produce about $5.2 million in additional revenues by next July. But even with the extra income, Metro could have an operating deficit as high as $4 million this fiscal year, according to General Manager Richard Page.

Page expressed optimism that the eight area governments that make up Metro would agree to cover the shortfall by increasing their subsidy payments. But if they don't, Page said, the system could be forced to cut its spending, perhaps resulting in service reductions.

Meanwhile, technicians have begun the job of reprogramming Metro's farecard gates for the new subway rates, which become effective Dec. 5, the day before the Red Line opens through to Van Ness. The new bus fares are to go into effect Dec. 6.

The major features of the new fare plan:

* During peak hours, rail passengers will pay 65 cents for rides of three miles or less, with 13 cents being added to the fare for every mile over three. This means peak-hour passengers going to Metro Center will pay $1.60 from New Carrollton, 90 cents from National Airport, $1.25 from Silver Spring and 70 cents from the Pentagon.

* During off-peak hours, Metrorail fares will be a flat 65 cents for rides of any distance.

* Bus base fares for peak hours will rise to 65 cents. Surcharges for crossing the District's boundaries also will grow, kicking fares to Maryland Zone 2 up to $1.50 and to Virginia Zone G to $1.30. The Virginia figure represents a combination of the base fare and the crossing charge.

* Metrobus off-peak fares will rise to a flat 65 cents in Virginia and Maryland but remain at 60 cents in the District. Off-peak trips across the District line will cost $1 to Maryland and $1.30 to Virginia.

* Passengers transferring from rail to bus in Virginia and Maryland will pay 40 cents as they enter the bus rather than the 65-cent base fare and an extra fee if they cross zone lines on the bus. In the District, the transfer will be worth the full bus base fare, with crossing fees extra. Proposals to charge 10 cents for bus-to-bus transfers were defeated by the board.

* Special fares for the elderly and handicapped, currently about half the normal rates, will stay at present levels for about 60 days pending study of a D.C. proposal to provide free rides within the city for these two groups.

* Most flash-pass prices will rise and free parking at Metro lots will continue on weekends.

The fare increases approved yesterday were less than Metro's staff had recommended. Board members said at the meeting that they raised fares reluctantly. They also agreed that the continuing cycle of raising fares to cover deficits could eventually make things worse by driving away riders.

Several members called for new efforts toward a regional tax devoted exclusively to transit, to give long-term financial relief. If no such solution is found, board chairman Joseph Alexander said, "we are going to price ourselves out of the business in the next two or three years."

Metro ridership dropped by about 2.6 percent in the last fiscal year, a trend blamed largely on two fare increases. It was the first annual drop in the system's history. The new increases, meanwhile, could drive ridership down by another 2 percent on an annual basis, Metro estimates.

Yesterday's 5-to-1 vote formally broke a deadlock that emerged last week pitting Maryland against the District and Virginia. Maryland wanted high base fares and low mileage charges for rail trips, which would favor its long-distance commuters. Virginia and the District, whose residents generally take short rides, argued for lower base fares and higher mileage charges.

The only dissenter yesterday was Dorothy Grotos of Virginia, who objected that the rail fare structure had been changed before the results of a special six-month study of operating costs were in.

In other Metro business yesterday, the board's budget committee endorsed a staff plan to concentrate federal funds for buses on refurbishing 600 buses already in the fleet, rather than buying new ones. With refurbishment costing about one-half of a new vehicle's purchase price, this is seen as a more efficient use of dwindling federal grants.