The biggest fare increase in Metro's history will take effect tomorrow morning when most bus and subway riders will find themselves paying between 5 cents and 25 cents more per trip.

About the only fare that will remain the same is the cost of a subway trip during nonrush hour. That stays at 50 cents for all trips regardless of distance.

Rush-hour subway fares, however, will increase by 22 percent. Thus, a ride will cost a minimum of 55 cents for three miles, plus 11.5 cents each additional mile. The automatic fare-collecting system, called Farecard, figures out the price of each trip and deducts it from the rider's ticket when he leaves the station.

Metro charges rush-hour fares on both bus and subway between 6 a.m. and 9:30 a.m. and between 3 p.m. and 6:30 p.m. weedays, excluding holidays.

Bus fares are increasing throughout the region. Also increasing are the costs of transferring from subway to bus. As is the case at present, there is no transfer credit for switching from bus to subway.

The fare schedule is so complicated and has so many variations that Metro has had to increase from three to five the types of two-week passes it sells just to cover the possibilities.

For the first time, however, the Virginia passes offer a genuine benefit (other than convenience) to those riders who use the sytem in rush hour both ways every weekday.

For example, a rider who uses both bus and subway to travel from Virginia Zone 1 to Metro Center with a transfer to the subway at the Pentagon will pay $22.50 over two weeks buying each fare separately. With the $16 Virginia two-zone pass, plus a $7 additional Farecard somewhere along the way, the total out-of-pocket cost will be $23, a savings of $2.50.

Similar savings are available with other Virginia passes. Maryland passes and D.C. passes offer somewhat less of a break, but add greatly to convenience for those who use the system every day.

Passes are available at more than 200 banks and five Metro sales outlets.

Subway fares for elderly and handicapped-riders will be half the regular rush-hour fare, to a maximum of 50 cents.

On Metrobuses, faces for the elderly and the handicapped will be 20 cents within the District of Columbia, 30 cents within the Virginia and Maryland, and 50 cents for any interstate bus trip.

The fare increases come at a time of dramatically rising costs in public transit. Transit authorities across the country are raising fares to record heights, partly because they can get away with it for the first time in years.

The price of gasoline and downtown parking has forced up the cost of driving an automobile even faster than transit fares can increase.

"We would normally expect to lose 6 million riders annually (out of 183 million) with a fare increase of this magnitude," Metro planner Bob Pickett said. "But those calculations don't mean anything now. We might lose 3 million; we might not lose anybody."

Higher fuel prices -- one of the reasons more people are riding mass transit these says -- are also contributing to the fare increases. Metro's cost for diesel fuel for its buses, for example, increased since last July 1 from 65.1 cents per gallon go 89.1 by the end of May.

Inflation -- another reason more people are riding public transit -- is also contributing to the fare increase. Starting Tuesday, Metro's bus drivers will receive a 37.5 cents an hour wage raise that will take their salaries to $10.235 an hour, or $21,288 a year.

That wage increase -- which Metro was ordered by an arbitrator to pay -- will cost Metro about $6 million in the fiscal year that begins July 1.Metro is hoping to win a reduction in the rate of increase -- which is determined by the Consumer Price Index for the Washington area -- in current contract arbitration proceedings.

The fare increases will provide a revenue gain in the year beginning Tuesday of $13.2 million, Metro planners said. Metro is projecting a record bus and subway operating budget of $271 million, revenues of $131 million and a deficit of $140 million.

That deficit, or subsidy, will be made up through a combination of federal, state and local aid. Without the fare increase, the deficit would have been $153 million. The D.C. deficit alone will be reduced by $4.3 million.