In an attempt to solve the problem of financing the Metro transit system through fare increases without penalizing those who can least affort to pay, the Arlington County Board has tentatively approved a system of half-price transit passes for low-income riders.

Arlington is the first jurisdiction in the metropolitan area to act on a transit subsidy proposal. County officials estimate it would aid more than 1,000 residents.

Under the plan the county would buy two-week passes for $10 apiece and sell them to residents for $5. The pass entitles the rider to unlimited bus rides in one jurisdiction and limited rail travel. A $16 pass, which the rider would buy for $8, would entitle the purchaser to limited rail travel and unlimited bus service between the Dstrict and Maryland and the District and the two nearest Virginia zones.

Implementation of the system depends on approval by the Metro board of a system of transit passes and fare increases that are expected to go into operation on July 1.

Residents who are eligible for food stamps, welfare or Arlington's tax and rent relief programs and who need public transportation to get to work would be able to buy the special half-price passes.

Each pass could be used by any member of the same family, Arlington County Board member Jospeh S. Wholey said.

Wholey, who is also Metro board chairman, said that the subsidy program, which he had proposed unsuccessfully for the past few years, "allows us to vigorously advocate a healthy increase in fares. However, we certainly recongnize the need of some people for help." Handicapped and elderly riders already receive reduced fares.

The county is still working out details of the plan.

Arlington is expected to officially adopt the half-fare program, on May 13 when it passes its budget for the next fiscal year beginning July 1. The program is expected to cost the county about $90,000 next year.

Adoption of the transit subsidy by Arlington is one solution to the regional political controversy that has surrounded fare increases and Metro financing.

For several years officials in the District have generally resisted fare increases while Northern Virginia riders have had to pay steadily higher fares. The Northern Virginia Transportation Commission has said that two-thirds of the cost of operating Metro should come from fares, not from revenue raised by property taxes.

Wholey who has said he is particularly concerned with reducing Arlington's property tax burden, advocates higher fares. He also proposed a number of subsidy programs now in operation for Arlington's low-income and elderly residents.

"The average commuter who uses public transportation has a higher family income than the average resident of Arlington or the metropolitan area. That makes me think that relatively high fares are not a bad social policy so the poor don't end up subsidizing the rich," Wholey said.