The commission that sets Northern Virginia's transit policy has recommended a series of proposals for the Metro system that would increase Metrobus base fares in the Virginia suburbs by 10 cents to 75 cents on April 2 and rail fares throughout the area by the same amount.

Under the proposals approved Thursday by the Northern Virginia Transportation Commission, the surcharge paid by Metrobus passengers for trips crossing the Potomac River to and from Virginia would go up by 10 cents to 75 cents, while zone fees in the Virginia suburbs would remain constant or would fall.

In addition, the Northern Virginia proposal would increase peak hour rail mileage rates for the Metro area. It would also replace the rail system's single fare system for weekend and off-peak rides by a sliding scale to make fares for longer trips more costly than for shorter ones.

All this is predicated on acceptance by the Metro board, which ultimately will receive various proposals from the area jurisdictions that use and finance operation of the bus and rail system.

The Northern Virginia commission, which sets transit policy for that area, does not have power to establish fares on its own. Its proposed fare package, however, will become the Virginia suburbs' official position when their Metro board representatives negotiate with D.C. and Maryland members over terms of a fare hike that the board is widely expected to approve for April.

Metrorail fares generally are uniform across the area and thus require agreement from all jurisdictions.

In D.C. and Maryland, governments generally have been more willing than Northern Virginia governments to provide higher subsidies to Metro and thus keep fares low.

The Metro board traditionally gives local governments the final word on bus fares inside their own borders, meaning the commission's rates for Northern Virginia could be close to those eventually adopted.

Under the plan, for example, a rush hour ride from the center of Springfield to the Pentagon, for instance, would go up to $1.25 from $1.20 cents, a 4 percent rise.

A ride from Alexandria and most points in Arlington during rush hour to downtown D.C. would increase from $1.60 to $1.75. One-way fare from Reston to downtown Washington would go up from the current $2.35 to $2.50.

The rush-hour charge for crossing any of the outer zone lines in Virginia would remain at 25 cents. The surcharge for entering or leaving Zone G, which includes Rosslyn and the Pentagon, would drop from 30 to 25 cents to bring it in line with other zone charges.

The base cost of boarding a Metrobus with a Metrorail transfer would rise from 40 to 50 cents. Charges for Metro's Flash-passes would also go up.

Northern Virginia Transportation Commission director David Erion said the increases would be borne most heavily by short-distance riders. This, he said is intended to give relief to those taking longer trips, whose fares have grown at a much greater rate than short-distance fares since 1975.

The per-mile surcharge tacked onto the base Metrorail fare after three miles of travel during peak periods would rise from the current 13 cents to 15 cents. That would raise the cost of a trip from Ballston to Metro Center from 90 cents to $1.05. From National Airport to Metro Center, the fare would rise from 90 cents to $1.00.

In addition, the commission suggested creating a 7.5-cent mileage charge for off-peak and weekend rail travel. That would push the cost of a Ballston-Metro Center ride from its current 65 cents to about 90 cents.