Can local governments run buses more cheaply than Metro? Last week, Fairfax County officially answered "yes." Fairfax supervisors voted to set up the county's own feeder bus network for neighborhoods near the Huntington Metrorail station, a move that may speed fundamental changes in the cost and quality of public transportation throughout the Washington area.

From the looks of it, Alexandria may follow suit. It would cancel some Metrobus service in the city, buy its own buses and put them on the streets. The result, city fathers hope, will be service that is cheaper and more responsive to local concerns.

In both jurisdictions, the target is the seemingly limitless subsidies: $135 million for the Metrobus system areawide this year. Pressure to do something is heaviest in Virginia, where local governments must pay most of their share out of general funds. Most of Maryland's bills are covered by state aid; D.C. has reserved special taxes for transit.

Officials in Fairfax and Alexandria are heartened by Montgomery County, which made the plunge in 1975 by creating its Ride-On bus system and has had only praise for it.

Still, the bus business is a costly and risky venture. It replaces the known, if high, cost of Metrobus with an unknown. It will require millions in capital funds for the buses, the hiring of large numbers of drivers and mechanics and facilities for maintenance and support.

Nonetheless, given the alternative, Metro-area governments increasingly are seeing the potential gains as worth the risk. Montgomery operates 93 Ride-On buses on 28 routes. D.C. has four routes for red-trimmed "Metro-Mini" buses. Prince George's County is interested, too.

If this trend continues, many transit planners believe, fundamental changes in Washington's public transportation structure will emerge a few years down the road, with Metro pulling back to running trains and longer-haul buses and local governments taking care of neighborhood service.

The Fairfax County plan calls for about 26 buses, costing about $4.2 million, to operate around the Huntington station, the southern end of the Blue Line. Opening date for the rail station is not fixed, but Metro is talking of late 1983 or early 1984.

A consultant's study estimated Fairfax could save big money doing the job itself--the equivalent of $600,000 of today's dollars a year over the next 20 years. Fairfax County expects to spend about $15 million of its own funds for bus and rail subsidies to Metro this fiscal year.

Alexandria's plan, which the City Council was to consider this week, calls for 18 buses, costing about $2.4 million. They would operate two routes to the Pentagon, one each from Eisenhower Avenue Metro station and downtown and two others in a northwest-southeast direction using the Braddock Road and Seminary Road corridors.

The savings, according to a consultant, would average at least $430,000 a year over the next 20 years. This year, Alexandria has allocated $5.7 million for payments to Metro for all purposes.

Both studies concluded there is money to be saved even if local governments have to pick up the full purchase price of the buses.

Why? Answers comes in various forms, but they boil down to escape from the Amalgamated Transit Union, which represents Metrobus drivers and mechanics, and escape from Metro's hefty overhead, much of it caused by federal regulations.

The ATU contract gives Metrobus drivers base pay of up to $24,825 a year, before overtime and other benefits are counted. Each quarter, the contract requires a increase equal to the full rise in the consumer price index. All told, personnel costs account for about two-thirds of Metro's total budget.

With a local bus system, the government's idea is to keep drivers and mechanics unorganized, or at least avoid the costly clauses in Metro contracts with unions.

Montgomery County's Ride-On drivers get a top base pay of about $18,000 a year. They are not unionized, although some drivers say pro-union sentiment is strong. In a referendum last year over whether to organize, drivers did not vote as a group but were lumped together with other blue-collar workers. The group as a whole voted not to unionize.

Metro also supports an enormous bureaucracy; its headquarters at Fifth and F streets NW takes up an entire city block. There are special offices for federal paperwork, public affairs, civil rights and governmental relations. Time-consuming hearings must be held to change routes.

Many of those are required as a condition for federal aid. By avoiding the federal aid, and the strings attached to it, the argument goes, costs can be kept down.

Instead of having its own legal office, a bus system can send its legal work to county attorneys. Paychecks would be issued by the local government's payroll office, not a separate one for bus employes.

Besides saving money, governments also want the freedom to set their own fares and routes without interference from the regional authority. They want smaller buses, driven and maintained by persons answerable to local officials, not to an impersonal agency across the river.

"Metro's bus plans just don't fit the small town local scene of Alexandria," Mayor Charles E. Beatley Jr. said.

Metro is not totally happy about all of this. For years, it has been buying buses and hiring drivers on the assumption local jurisdictions would want service. But if the locals can do the job cheaper, Metro officials concede, they can't be expected to remain loyal.

In the long run, however, decentralization could work in Metro's favor. The loss of driver jobs could give new clout in negotiating with its unions. The competition might shake it out of a long lethargy brought on by its monopoly on public transit.