By a vote of 5 to 3 the Fairfax County Board of Supervisors this week approved a Metro proposal setting out where commuters will transfer from buses to trains when the expanded Metro system begins in July of this year.

The supervisors, however, gave their approval with strings attached. They stipulated that a formula allocating shares of the operating deficit for the Metro system to the participating jurisdictions must be drawn up and approved by them before the July opening of the expanded rail system.

Under the plan approved Monday, Virginia riders will transfer from their buses to trains at the Pentagon, at National Airport and at Rosslyn. Buses which do not pass near a Metro train stop on their present runs into Washington will continue to bring their passengers directly into the city.

The Virginia section of the suburban bus-and-train meeting-place plan had been held up at least two weeks pending the Fairfax County supervisors' approval, said the county's transportation planner, Shiva K. Pant.

Board chairman John F. Herrity and supervisors Marie B. Travesky (R-Springfield) and Audrey Moore (D-Annandale) voted against the commuter transfer plan.

Herrity said he would not vote for it because participation in the transfer to the rail service "would make the county liable for participating in the debt service of the Metro system."

Moore said she opposed the plan for the same reason and on the grounds that it was "inconvenient" to commuters who would be forced to transfer to a train instead of having the opportunity of remaining on a bus all the way to work. Moore said that although the new bus-train combination would take less time, the commuter "would be interrupted in his work" that he would be doing on the bus in order to transfer to the train.

Supervisor John P. Shacochis (R-Dranesville) said that "every time we bring up Metro we see some insidious plot against Fairfax County and that's not the case."

Pant said the county could not afford to have a "double option transit system" in which the commuter can choose if he will ride a bus all the way or transfer to a train. The bus-to-transfer, Pant said, "was planned all along; it is not an 11th hour idea."

In other matters last Monday, supervisor Alan D. Magazine (D-Mason) asked the staff to look into why an advertisement for architectural bids for the new courthouse appeared in area newspapers before the referendum last Feb. 22. Voters in the referendum approved the county's purchase of long-term bonds to finance construction of a new courthouse.

"If anything destroys the credibility of government, it's this," Magazine said, referring to the fact that the advertisement appeared before the voters approved construction of the building.

Supervisor Martha V. Pennino (D-Centreville) said she had come across a "zoning loophole" which permits the keeping of farm animals in half-acre subdivisions. The zoning laws do not rule out the keeping of animals such as horses as long as the owners property is at least 80,000 square feet.

Calling such a condition "a public nusiance and possibly a health hazard," Pennino asked the staff to submit an ordinance to the board which would eliminate this "loophole."

"Now that we're an urban county we're going to have these problems," Pennino said.

Finally, the staff was asked to consider how the board should deal with requests for specialized sports facilities, such as skateboarding rinks and motocross bike trails. There has been an increase in such requests.