The Metro board voted yesterday to adopt a simple subway-to-bus transfer system starting July 1 instead of a method that was sharply criticized at public hearings as being too complicated.

Under the adopted system, a passenger entering and paying a train fare at a Metrorail station will get a transfer free of charge from a vending machine. The transfer will be good for a ride worth up to 50 cents on a Metro-bus. Extra suburban zone charges must be paid in cash.

There will be no such transfer arrangement for passengers riding in the other direction, changing from a bus to a train, since the new Metrorail electronic fare-collection equipment cannot be adapted to accept paper transfers. Two full fares must be paid.

The system approved yesterday will give a typical round-trip passenger a discount of 50 cents below what would be paid if fares for two bus rides and two train rides were collected individually. The Metro board is considering a commuter pass that would give regular riders a 75-cents daily discount.

Even with the 50-cent discount, riding a Metrorail train will be costly for many riders as compared with an all-bus trip. For example a round trip to the Federal Triangle from the Walter Reed Hospital area, by bus and rail, transferring at the Takoma station, will cost $2.20. The bus now costs 80 cents, but the fare may rise July 1 to $1.

The transfer system will go into effect July 1 when Metro opens its second 12-mile rail line from the Stadium-Armory station through downtown Washington to the National Airport station in Arlington.

The transfer system also will be used on the existing 5-mile downtown subway and its Silver Spring extension, tentatively scheduled to begin service next Nov. 1.

The free rail-to-bus transfer system was adopted in place of method that would have required an inbound passenger to get a special transfer on the bus in the morning, carry it all day, get it validated by a stamping machine on the way home in the evening and ultimately to use for a free bus ride.

There were two justifications given for the complex proposal.

It was intended to give a discount fare only to round-trip passengers, which will no longer always be the case. And it was designed to prevent transfer give-aways.

Although the complex system was criticized by numerous witnesses at public hearings, it was not its complexity - but rather the lack of time to buy and install the validation equipment - that led to yesterday's decision.

In proposing the simple transfer, Joseph S. Wholey, Metro's first vice chairman, said it would be experimental, subject to later change if it fails to work or is abused.

On another matter, the board received a resolution from the Fairfax City Council asserting its refusal to share in Metrorail deficits because the trains do not serve the ommunity. Fairfax County Supervisor John P. Shacochis, a Metro board member, said the board should take steps to expel Fairfax City from its Metro partnership. A board committee will consider the issue.